To what degree could a person be "pro-polygamy" yet still obey the LDS church?

Edits: So, after the question changed... here's the answer to the new question; my original answer is below... though they do mingle some similar points and should both be considered.

This answer reflects my own thoughts on the matter, but I'm of course no clergy in the LDS Church...

New Answer

The LDS Church doesn't hold opinions against anyone. Everyone is entitled to have an opinion. However, as Christ teaches, we are on safer and higher moral ground when we align our thoughts, hopes, desires, and actions with those of the Savior's. When these are in harmony, there is peace and happiness. When there is friction, often there is temptation and a slippery slope.

The LDS Church teaches to stay away from the edge, not see how close you can get to it. In general, I would expect this thinking/hoping to be strongly discouraged by the LDS Church...

Your question (now) is more about whether the thoughts/desires are transgression of the law or acting out is transgression of the law. However, still the same as my answer below about excommunication, it varies per circumstance and no one can judge but a judge in Israel (again, in LDS theology this is a bishop) and the Lord.

I see little difference between this type of thinking and the thinking of something like, "I hope that I can lay with that woman" -- or -- "I want God to tell me to sleep with her." These thoughts, of course, are (implicitly) adulterous, and this in the heart is also a sin.

A prophet in the Book of Mormon warns:

30 But this much I can tell you, that if ye do not watch yourselves, and your thoughts, and your words, and your deeds, and observe the commandments of God, and continue in the faith of what ye have heard concerning the coming of our Lord, even unto the end of your lives, ye must perish. And now, O man, remember, and perish not.

Finally, and this makes reference to a piece from earlier and below, the temple recommend interview questions include a question about sympathizing with groups or individuals who have teachings contrary to the Church. For Mormons to be able to enter the temple, they must make sure this is not the case.

Original Answer

I see this question as more about excommunication than polygamy, essentially wondering, "How close to the edge can you get without falling off?"

Naturally, LDS Church leaders have taught against this mentality: stay well within the bounds of the Lord's commandments. Some risks are just not worth taking. Jesus taught this in His higher law: Don't merely love your friends and hate your enemies, but bless them that curse you, do good to them that hate you, and pray for them which despitefully use you and persecute you. Also His command to not merely not kill somebody, but do not even be angry with them. Stay well away.

Above, you present 3 ways in which somebody might tread too close. In situations 1 and 2, the thoughts or desires of the person is contrary to God's commandments, but is not actually acting outright, as the person still apparently wants to stay within the bounds the Lord has set. This behavior of course, requires repentance, as the person is asking either for permission to break God's law or for God to change His law. Martin Harris did the same thing during the restoration of the Church with the 116 pages which became lost in consequence. God commanded both Him and Joseph Smith to repent.

In all of the above situations, especially the third, the person could potentially be acting out publicly: by means of political activism, or groups or "clubs" or other various ways of expressing his opinion publicly or to rally others for a cause.

In the temple recommend interview questions, a person is asked something like if they are affiliated with, support, or sympathize with any groups or individuals which oppose Church teachings. Of course, temple worthiness is on the far opposite end of the spectrum from excommunication: one who may not enter the temple may not be near disciplinary action. This question is in place for a very important reason, though (obviously) -- one cannot have one foot in Zion and another in Babylon: a house divided against itself will fall. The person, acting in public on his desires, and thus acting upon the temptation to desire that which is contrary to the Lord's commandments, is probably committing sin...

Now, excommunication is a personal ordeal for which its reasons vary widely, but in general it is done only to help the person repent and suffer less condemnation in the process. I cannot say whether the person in any of the 3 scenarios above would be excommunicated, except that I think, probably not, unless the person knew full well what he was doing was contrary to the Lord's commandments and he was coming out in open rebellion against God, was setting a bad image for members of the Church and the Church itself, and was essentially ruining his own life and trying to bring others down in the process.

This is rarer than than common for sure, as everyone is tempted to do evil: it is acting on it, and the degree and circumstances upon which we do the action, that is all considered to be needful of repentance, and only the Lord and His appointed judges in Israel (in LDS teaching, the Priesthood leaders such as bishops) can really judge. I'm sure that a bishop would counsel with a member who is indulging in such thought or activity, but disciplinary action entirely depends on the situation, and again, is more rare than common.

For more information:

http://www.lds.org/scriptures/dc-testament/od/1 (Official Declaration 1, about practicing polygamy, by Wilford Woodruff.)

http://www.mormonnewsroom.org/topic/polygamy (Newsroom article: Polygamy)

http://www.mormonnewsroom.org/article/why-is-a-mormon-excommunicated (About excommunication)

http://mormon.org/faq/topic/polygamy (Do Mormons practice polygamy?)