The term you're looking for is trans, not trap. Traps are fictitious sexual fantasies and do not necessarily conform to their expressed gender. Now, you have two options there, a character that's trans_gender_, which probably means that their identity be left to their lore and not be some out-in-front show for everyone. Or you can go with trans_vestite_ which is someone who dresses themselves as the opposite sex, but still associates themselves as their original gender (i.e. Eddie Izzard).
I personally wouldn't mind a character who maybe dressed in different gendered outfits or presented themselves in a more progressive way. Transvestism is a fairly interesting topic when discussing gender identities. Showing off the modern nature of how "boys can wear dress' too."
An actual transgender character, however, would be very difficult to properly pull off for a number of reasons.
If you establish them as one gender and then give them tells that they used to be another gender, then it makes them more of less the butt of a joke regarding non-passing transfolk, which doesn't exactly need any help in that arena.
I think it would be much easier to have a character explore their identity through their dialogue. There's a much less likely chance of it blowing up in Riot's face.
Sincerely,