If the kit is close enough, you can just use a heat gun to heat it up and bend it into shape. If it's too off, you'll have to cut and re-glass sections, which is usually only need on shitty kits. If you're going with a urethane kit and it doesn't fit correctly, you're screwed, because it's impossible to alter them. IMO, a kit is never going to fit as good as OEM though, so learn to not nit-pick too much because you'll drive yourself crazy. Get the kit fitting the way you want it, take it off and have it painted (unless you're painting the entire car), re-install it. You're done.