Actually, I might accept someone as being something they literally aren't if they've spent long enough living full-time as that other thing. So if a non-white person continuously presents as white, self-identifies as white, and is treated by everyone else as white, I might consider the person white if this goes on for long enough, since for day-to-day interactions the person may as well be. (I won't say anything about people "transitioning" to races other than my own.)
I saw this criterion in the article supporting transracialism that caused so many SJW-type people to flip out; it's in the paragraph starting "I do not think so."
http://onlinelibrary.wiley.com/doi/10.1111/hypa.12327/full
As she says at around that point, this criterion might allow somebody to change their gender or race, but it probably wouldn't allow somebody to become a cupcake, since it's hard to see how somebody could convincingly present as a cupcake to other people.