It really depends on what it is. If I were overweight and he wanted me to lose some for my own health, I'd do it. If I'm just a little plushy and he wants me to lose weight just to be nicer to look at, then he's kind of an ass.
That's honestly the only thing I could see him asking me to change, if I were overweight and needed to lose some. And quitting smoking. I know he'd like me to do it, but I don't smoke much to begin with, so he doesn't hassle me about it.
Things like hair color and colored contacts? I do that all on my own for fun. I'm out of colored contacts but I like the ones for astigmatism better, my vision is a lot crisper and clearer. And my hair, well, right now my hair is a gorgeous shade of purple that he absolutely loves. I've been with the guy that wanted me to keep it brown, I left him. Not over that specifically, but that was part of it.