The best advice I can give is to ask your surgeon. I don't know your age (which may be the reason for the white hairs if you are older), but what you have to remember is that when your hairline is lowered, what is actually happening is that your scalp is being stretched and each individual hair is slightly further away from its neighbour. So there is obviously a limit to how many times this process can be repeated, if indeed it can in your case.
You may get an answer from somebody who has had it done and it has been successful, but that doesn't necessarily mean it would be successful in your case.
Quite simply it's best to speak to your surgeon.
Regards
Caroline