Hmmm, reckon you'll need paint after you mod it that way mate.... I've heard that if you heat the metal up a bit with a hot air gun you might soften the paint enough to not crack it, but whatever you bend it with will probably mark it anyway....
And, if you bend the arch up and out, wont the plastic want to come up and out with it? There's a lip on the inside of the plastic molding that attaches to the inner lip of the wing isn't there?