Role-playing another person is fine. But don't try to replace your real self, and don't do it to try to make friends, because you want your friends to know the real you instead of some persona you put on to deal with a tough spot.
If you want to bring out your inner Sheldon when you try to understand something tricky, or pretend you're a gangster if you have to confront somebody, that's cool. but remember--it's really just a mental trick to get yourself in a frame of mind where it's easier to do something. When you get right down to it, you're doing things you're capable of doing without play-acting. You're just holding a magic feather, really.