After WWII, a bunch of Germans packed their things and moved to Argentina. They weren't Germans anymore. They became South Americans. Thus a person can change his or her race if s/he wants to. It's all subjective anyways, so what's wrong with changing it subjectively?

As for wanting to be a horse, that is like being trans. Your mind doesn't match your body. If you want to run in the Kentucky Derby, fine. Just don't be mad when you get trampled and undoubtedly change your mind.