Do Christian groups which think homosexuality is a sin think you can be a practicing homosexual and also a Christian?

As for just your header question, the answer is simple - no.
My answer to your next question will explain more detailed about it.

As for your next questions in the body (How do these groups handle the question of whether a person can be both a h*m*sexual and also a Christian? & Are there any additional steps required?), I explain to you here:
All the christian should seek, is to be approved by the Father. And the approval we can get only by doing His will. (This is where I fully agree with you that all the christians should do what the Bible says to do, apply all the divine principles in their day-to-day life.) And the faith needs to be proven, as we can see from the last part of this verse: Genesis 17:1
(NWT)

When A′bram got to be ninety-nine years old, then Jehovah appeared to A′bram and said to him: “I am God Almighty. Walk before me and prove yourself faultless.

(CEV)

Abram was ninety-nine years old when the LORD appeared to him again and said, "I am God All-Powerful. If you obey me and always do right,

The word of God in the Bible clearly states that the h*m*sexuality is detestable to God eyes, and that God therefore condemns h*m*sexuality.
It's clearly explained in Richard's posted answer on another related question.

Being christian is not easy, specially as we are imperfect and being taunted and tempted by Satan the Devil day by day, as this wicked system of things draws closer to its conclusion. Now you may want to do some BIG changes in your life, as per to be approved and allowed into His new upcoming Kingdom in a restored paradise.
God is All-Powerful. Just pray for He give you the Holy Spirit to help you to dress up with the new personality. Be specific, ask. And you'll be heard. Pray from your whole heart, whole mind and whole soul full of faith and hope (not doubt). And remember, God is kind to patient, faithful and discreet servant. May God Bless You!

As for your last question Do these groups teach that it would be sinful to continue practicing after one became a Christian?, there are no fitting answer (As from my point of understanding). And that is because one cannot become a Christian until he\she completes certain requirements, stop being h*m*sexual in this case.

I just genuinely want to help you. In any case I want you to have your own opinion and to decide for yourself, instead of accepting my or other people viewpoints and understandings (regardless of what the majority or the authority has to say).

I declare to you, brothers and sisters, that flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable. (1 Corinthians 15:50 NIV)

Man is composed of flesh, soul, and spirit. The spirit preserves and fashions the temple of flesh. Between these two is the soul. When the soul follows the spirit, is raised up by it, but sometimes it sympathizes with the flesh, and falls into carnal lusts.

So I say, walk by the Spirit, and you will not gratify the desires of the flesh. (Gal 5:16 NIV)

Those then, as many as they be, who have not that which saves and forms us into eternal life, shall be called, "flesh and blood" for they do not have the Spirit of God in themselves. Men of this type are spoken of by the Lord as "dead".

But Jesus told him, "Follow me, and let the dead bury their own dead." (Matt 8:22 NIV)

He calls them dead because they have not the Spirit that quickens a man.

As for you, you were dead in your transgressions and sins, in which you used to live when you followed the ways of this world and of the ruler of the kingdom of the air, the spirit who is now at work in those who are disobedient. All of us also lived among them at one time, gratifying the cravings of our flesh and following its desires and thoughts. Like the rest, we were by nature deserving of wrath. (Ephesians 2:1-3 NIV)

On the other hand, as many as fear God and trust in His Son's advent, and who through faith do establish the Spirit of God in their hearts,-such men as these shall be properly called both "pure," and "spiritual," and "those living to God," because they possess the Spirit of the Father, who purifies man, and raises him up to the life of God.

No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person's praise is not from other people, but from God. (Romans 2:29 NIV)

For as the Lord has testified:

"Watch and pray so that you will not fall into temptation. The spirit is willing, but the flesh is weak." (Matthew 26:41 NIV)

So "the flesh is weak," but also "the spirit is willing." For the spirit is capable of working out its own suggestions.

Therefore, if anyone were to mix the ready inclination of the Spirit, to be as it were, a stimulus to the infirmity of the flesh, it inevitably follows that what is strong will prevail over the weak, so that the weakness of the flesh will be absorbed by the strength of the Spirit; and that the man in whom this takes place cannot in that case be carnal, but Spiritual, because of the fellowship of the Spirit.

Therefore the martyrs bear their witness, and despise death, not after the infirmity of the flesh, but because of the readiness of the Spirit. For when the infirmity of the flesh is absorbed, it exhibits the Spirit as powerful; and again, when the Spirit absorbs the weakness [of the flesh], it possesses the flesh as an inheritance in itself, and from both of these is formed a living man,-living, indeed, because he partakes of the Spirit, but man, because of the substance of flesh.

The flesh, therefore, when destitute of the Spirit of God, is dead, not having life, and cannot possess the kingdom of God: as it is irrational blood, like water poured out upon the ground.

As was the earthly man, so are those who are of the earth; and as is the heavenly man, so also are those who are of heaven. (1 Cor 15:48 NIV)

In the case of Martyrs the rational blood is preserved by God for the avenging of those that shed it.

Do not take revenge, my dear friends, but leave room for God's wrath, for it is written: "It is mine to avenge; I will repay," says the Lord. (Romans 12:19)

The flesh possessed by the Spirit, forgetful indeed of what belongs to it, and adopting the quality of the Spirit, being made conformable to the Word of God.

And just as we have borne the image of the earthly man, so shall we bear the image of the heavenly man. (1 Corinthians 15:49 NIV)

What, therefore, is the earthly? That which was fashioned. And what is the heavenly? The Spirit.

But now, by dying to what once bound us, we have been released from the law so that we serve in the new way of the Spirit, and not in the old way of the written code. (Romans 7:6 NIV)

Or don’t you know that all of us who were baptized into Christ Jesus were baptized into his death? We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life. (Romans 6:3-4 NIV)

...He saved us through the washing of rebirth and renewal by the Holy Spirit (Titus 3:5 NIV)

The apostle exhorts us through faith and chaste conversation to preserve the Spirit of God.

May God himself, the God of peace, sanctify you through and through. May your whole spirit, soul and body be kept blameless at the coming of our Lord Jesus Christ. (1 Thessalonians 5:23 NIV)

Unless having become non-participators of the Divine Spirit, we lose the kingdom of heaven.

But the subjects of the kingdom will be thrown outside, into the darkness, where there will be weeping and gnashing of teeth." (Matthew 8:12 NIV)

And he exclaims:

I declare to you, brothers and sisters, that flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable. (1 Corinthians 15:50 NIV)

Speaking strictly, we would say that the flesh does not inherit, but is inherited; as also the Lord declares:

Blessed are the meek, for they will inherit the earth. (Matthew 5:5 NIV)

As if in the future kingdom, the earth, from where exists the substance of our flesh, is to be possessed by inheritance. This is the reason for His wishing the temple (the flesh) to be clean, that the Spirit of God may take delight therein, as a bridegroom with a bride. As, therefore in old Jewish tradition, the bride cannot be said to wed, but to be wedded, when the bridegroom comes and takes her, so also the flesh cannot by itself possess the kingdom of God by inheritance; but it can be taken for an inheritance into the kingdom of God. For a living person inherits the goods of the deceased; and it is one thing to inherit, another to be inherited. The former rules, and exercises power over, and orders the things inherited at his will; but the latter things are in a state of subjection, are under order, and are ruled over by him who has obtained the inheritance.

What, therefore, is it that lives? The Spirit of God, doubtless. What, again, are the possessions of the deceased? The various parts of the man, surely, which rot in the earth. But these are inherited by the Spirit when they are translated into the kingdom of heaven. For this cause, too, did Christ die. That the Gospel covenant being manifested and known to the whole world, might in the first place set free His slaves; and then afterwards, as I have already shown, might constitute them heirs of His property, when the Spirit possesses them by inheritance. For he who lives inherits, but the flesh is inherited. In order that we may not lose life by losing that Spirit which possesses us, the apostle, exhorting us to the communion of the Spirit, has said, according to reason, in those words already quoted, "That flesh and blood cannot inherit the kingdom of God." Just as if he were to say, "Do not err; for unless the Word of God dwell with, and the Spirit of the Father be in you, and if you shall live frivolously and carelessly as if you were this only, viz., mere flesh and blood, you cannot inherit the kingdom of God."

So no. A h*m*sexual sympathizes and is in communion with the flesh, and therefore does not have the Spirit. For the flesh is not buried with Jesus. Nor are the sins covered.

If we have been united with him like this in his death, we will certainly also be united with him in his resurrection. (Romans 6:5 NIV)

So if the imperishable never inherits the perishable. The perishable remains perishable and perishes.

Then death and the grave were thrown into the second death. (Revelation 20:14 De-Analogized)

Reference:
[1] Chapter IX
http://www.earlychristianwritings.com/text/irenaeus-book5.html

The Apostle Paul seems to address this particular question quite specifically:

Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice h*m*sexuality, 10 nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God. 11 And such were some of you. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God. 1 Corinthians 6:9-11 ESV

Here, h*m*sexuality is mentioned along with quite a few other things like adulterers, thieves, and even greedy people.

So, it seems that no matter what anyone has ever been or done, that person can still be washed, sanctified, and justified (declared righteous) in the name of the Lord Jesus Christ. This person will become a new creation in Christ (2 Corinthians 5:17), be indwelt by the very Spirit of God (1 Corinthians 3:16), and become a child of God (John 1:12-13).

As a child of God whose body is a temple of the Holy Spirit, God calls us to live a holy life. Such a life should be free from all of the things Paul mentions. Thus the thief should steal no more, the drunkard should become sober, the adulterer should be faithful to his wife, the greedy person should become a generous giver, and the sexually immoral should live in purity.

So, from one perspective (but not all) that takes a literal reading of Scripture, anyone can become a Christian--a mass murderer, a rapist, a thief, a greedy person, an adulterer, or someone who practices h*m*sexuality. Once a person has come to Christ, though, God desires them to live a holy life and indicates that certain things should no longer be practiced.

1. What you "are" is irrelevant

Let us first distinguish between being a member of a class - in this case h*m*sexuals - and engaging in any sort of behavior. For many people, being a member of the class "h*m*sexual" means having feelings in one direction or another. In no event would a "temptation" towards a certain behavior be taken as exclusion.

James makes it clear that temptation itself is not sin.

Galatians also makes it clear that being a member of any class is irrelevant:

26 So in Christ Jesus you are all children of God through faith, 27 for all of you who were baptized into Christ have clothed yourselves with Christ. 28 There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus. 29 If you belong to Christ, then you are Abraham’s seed, and heirs according to the promise.

At the risk of self promotion, look at this answer for more.

2. What you do is irrelevant

Even without broaching the question of whether or not h*m*sexual activity is sin, this question still be categorically answered "Of Course you can!"

The primary message of the Gospel is grace. Grace is God's unmerited favor - the free gift that he bestows in which he says "You are forgiven"

Remember that before God ALL MEN ARE SINNERS. As Isaiah 64:2 says, eve "our righteousness is as filthy rags" in God's sight. There is simply no person that God loves more than any other - he is "no respecter of persons"

Furthermore, as Ephesians 2:8-9 states,

"For by grace you are saved through faith - it is NOT through any work of your own, lest any man should boast." Since there is nothing that you do to earn your salvation, your status is irrelevant.

3. Whether or not you continue in h*m*sexuality is the only question

Once one is a Christian, one is expected to grow in Christ - to become more Christ-like. Here is where as you mature, you may want to put these things away. But, understand, obedience comes out of love and desire to be more like Christ.

As Jesus says in John 14:12 "If you love me, keep my commandments." It is explicitly not "Do what I say so that I will love you."

Under no circumstances should one believe they need to get clean before being washed by Jesus!

Finally, what you probably want to ask is "Is Homosexuality a Sin" This question has been asked here and here. Gene Robinson, the Episcopalian bishop of New Hampshire who left his wife for another man likes to argue Acts 10 - (Let no man declare unclean what God has declared clean) - that God is doing a new thing. I personally don't think God's word has changed on that matter - but I bring it up to say that Christians debate the matter.

In any case, sin is irrelevant. God's grace is what is important.

Of course you can be whatever you want and be a Christian. The question is whether or not God will leave you that way.