I'm sure to even a beginning med student those differences would not be subtle at all, and it would take most of them about a nano-second to figure it out (or at least to form a hypotheses, and start to test it). We are talking about people in med school, who for the most part were the best students in the really hard classes.
That, and once you're all cracked open there on the table you ain't got that many secrets left to conceal.
And, most institutions taking a body will wait for it till after your family has its way with you (i.e. they will wait till after the funeral). There is no rush, you're already dead, and its unlikely you're going to get any better.