What are the teachings of Catholic Church on the implications of gender-change by individuals, in their life-after-life?

There are verses in the Bible that allow a reading of God as androgynous (i.e. both male and female). Since Genesis 5:12 claims humans are made in the image of God, such a reading renders human gender change void of implications.

Such a reading is not accepted by most denominations, including Catholic authorities, who insist gender change does not change anything in the eyes of the Church. See:

Male and Female He Created Them: Towards a Path of Dialogue on the Question of Gender Theory in Education

Isaiah 42:14

I have kept silent from ages past; I have been quiet and restrained Myself. But now, I will groan like a woman in labor, gasping breathlessly.

Isaiah 49:15

Can a woman forget her nursing child, or lack compassion for the child of her womb ? Even if these forget, yet I will not forget you.

Hosea 13:8

I will attack them like a bear robbed of her cubs and tear open the rib cage over their hearts. I will devour them there like a lioness, like a wild beast that would rip them open.

Numbers 11:12

Did I conceive all these people ? Did I give them birth so You should tell me, ‘ Carry them at your breast, as a nursing woman carries a baby,’ to the land that You swore to give their fathers?

Deuteronomy 32:18

You ignored the Rock who gave you birth; you forgot the God who gave birth to you.

Furthermore, God is described as breastfeeding new believers in several verses:

1 Peter 2-3:

Like newborn babies, crave pure spiritual milk, so that by it you may grow up in your salvation, now that you have tasted that the Lord is good.

1 Thess 2:7-8

Instead, we were like young children[a] among you. Just as a nursing mother cares for her children, so we cared for you. Because we loved you so much, we were delighted to share with you not only the gospel of God but our lives as well.

1 Cor 3:1-3

Brothers and sisters, I could not address you as people who live by the Spirit but as people who are still worldly—mere infants in Christ. 2 I gave you milk, not solid food, for you were not yet ready for it. Indeed, you are still not ready. 3 You are still worldly. For since there is jealousy and quarreling among you, are you not worldly? Are you not acting like mere humans?

Heb 5:12–13

In fact, though by this time you ought to be teachers, you need someone to teach you the elementary truths of God’s word all over again. You need milk, not solid food! 13 Anyone who lives on milk, being still an infant, is not acquainted with the teaching about righteousness.

1. "Sex-change operations" are mutilations of the body, changes in the accidents (not substance) of a human.
   (The soul doesn't have a sex; St. Ambrose On Virginity ch. 15: "anima enim sexum non habet", "for the soul doesn't have a sex".)

2. Only scars of wounds, not lost limbs or major mutilations, can remain in resurrected bodies, as St. Thomas writes in Summa Theologica suppl. q. 82 a. 1 ad 5:

   The scars of wounds will not be in the saints, nor were they in Christ, in so far as they imply a defect, but as signs of the most steadfast virtue whereby the saints suffered for the sake of justice and faith: so that this will increase their own and others' joy (cf. q. 54 a. 4 ad 3). Hence Augustine says (De Civ. Dei xxii, 19):

   We feel an undescribable love for the blessed martyrs so as to desire to see in that kingdom the scars of the wounds in their bodies, which they bore for Christ's name. Perchance indeed we shall see them for this will not make them less comely but more glorious. A certain beauty will shine in them, a beauty though in the body, yet not of the body but of virtue.

   Nevertheless those martyrs who have been maimed and deprived of their limbs will not be without those limbs in the resurrection of the dead, for to them it is said (Lk. 21:18): "A hair of your head shall not perish."

3. ∴, the sex of humans with their resurrected bodies will be that in which God created them.