>>40302780every human's genome has all the necessary genetic information to produce a male or a female (this is obvious for XY, but the SRY gene is really just a switch, all the genes governing stuff downstream of it are still there in cis f XXs and just not active in that particular way)
this makes the claim "i have a ~male brain despite the fact that my body looks female" or vice versa prima facie plausible, and is also the reason HRT works.
this is not true for race. white people don't have a bunch of latent genetic pathways that will cause them to start looking like black people if you inject them with melanin. the correct, though of course not perfect, racial analogy to transgender people is mixed-race people choosing one part of their ancestry to identify with more than the others.
that said, there's no reason to stop people from pursuing procedures intended to make them look like a different race. people can do what they want with their bodies. there's just not an underlying medical anomaly like there is with gender dysphoria.