Started to read through the invocations (didn't get further than the bit that gives them invocations in the first post of the class). "Rogues Cunning" could be argued to persist in its effects even after being swapped out for another invocation (but it could be dispelled?). I would say if you swap it out then you keep the disable device ranks (but it doesn't count as a class skill for adding more, meaning you have to double your total class levels before you can add any more skill points), and you lose Trapfinding. Alternatively just say that it CAN'T be swapped out.