I don't change finished works, even when I sometimes bleed and cringe at what I've done, b/c in some ways I feel like you have to hit a point where something is done, flawed or not. If you know the flaw is there, that's the important thing -- not because you're going to "fix" something that's out, but because you'll do it better next time. And it's worth preserving the mistakes for no other reason than to remind myself that I make them, and Feel The Cringe.