Those who espouse “transgenderism” argue that a human person is assigned their gender at birth, based on their observed anatomy. Consequently, when a biological male identifies as female and then has related surgery, they speak of that medical practice as “gender confirmation” vs. “gender reassignment,” because they believe their anatomy now reflects their true identity as a human person.
The Church has a different take, one that is grounded in genuinely confirmed reality. One is born either or male or female, and this also applies to hermaphrodites who, though they manifest both male and female anatomical aspects at birth, are either biological boys or girls.
In this light, the Church recognizes that every human person is created in the image and likeness of God, male or female (Gen. 1:26-27). And so we should help people discover their true identities as children of God, not support them in the disordered attempt to reject their undeniable biological identity.
In this light, we should act in love toward those who experience gender identity disorder, and reprove those who engage in name-calling and other uncharitable behavior toward them.
Regarding preferred pronouns, I would advise avoiding that problem and just call the person by their preferred name. Let me give an example. In previous work for the Church, I once received a phone call from a man who had had “sex-change” surgery and now identified and lived as a woman. He referred to himself as “Mary” (not the person’s self-identified name). I saw no point on first introduction over the phone to tell him I wanted to know the name his parents gave him at birth, and that I would only and always refer to him via that birth name during our conversation, lest I transgress and affirm him in his gender identity disorder.
Well, had I followed such pastorally misguided advice, that would’ve been a real short conversation. In addition, this person was calling a faithful Catholic apostolate to receive genuinely Catholic counsel, not persuade me to affirm them re: their self-identified gender. If I wanted to have hope of giving a fruitfully faithful witness, I couldn’t let minor details derail my witness. In other words, I couldn’t let style get in the way of substance.
Rather, while using this person’s preferred name, I lovingly explained how they had to live a chaste life, which in their case meant not simply ending a sexually intimate relationship with a Christian man who wanted to continue the relationship despite having learned about Mary’s surgery, but refraining from dating altogether and living a life of complete continence.
As a result of my witness, which included fundamentally reminding them that Jesus really loved them amidst their struggles, they gratefully recommitted to living a chaste life. (On a related note, given the expense and potential psychological trauma involved, the Church would not require a person who had had “sex-change” Church to have a second surgery to reverse that change.)
If we give faithful witness to the teachings of Christ and his Church, then using a person’s preferred name will become a moot point. In contrast, if we insist at the outset on setting them straight on which name we will use to refer to them, we will likely lose the opportunity to give them a faithful witness through which Christ can soften their heart to receive and embrace the true Gospel.
And if they correct you on calling them “Mr.,” “Miss,” etc., circumvent that issue by asking them their name, which will likely reflect their self-identified gender. And then proceed in Christian love from there.