There's a difference between finding enjoyment in transgressing lines of expectation in outfits, and finding the experience of your body and social place as wrong, and wanting to change it to better fit with who you are. Yes, for people young enough, gender affirmation largely lies in changing clothes, names, pronouns, but over a lifetime it usually doesn't stop there. Having your body start shifting on you, in ways that aren't congruent with your experienced gender, is godawful and horrifying. Imagine your experience of puberty, but instead of the hormone you had dominant in yours, you got the other one.
You can go ahead and ask me anything about the experience; I was one of those kids, before affirming care was a thing for kids, and my goddess did it suck, and I suffer fallout from it still.
Any sufficiently identical copy of me is me. A copy just means there are more me in the universe.