When it comes to maneuvers, you can learn them while evil and still retain it even if you turn(actually same goes for spells...). It's the same as a skilled serial killer converts to a life of virtue, but he still know a hundred ways to skin a man and turn it into a nice pair of pants. If he's put into a situation where he NEEDS that knowledge, he'll probably use it.
And there is a mechanic for unlearning maneuvers by replacing it at 4th level and every even level thereafter(I houserule it's based entirely on initiator level, not just core class).