To be fair Cherokeesam, I don't think it would ever happen like that. Any tweaking or such to the film would involve Black co-ordinating with Feige and Marvel who in turn would co-ordinate with Wright and vice versa. Nothing would be allowed to happen that would upset the apple cart. If Black had an idea that he thought was great for Ant Man or something, he'd probably already be well aware of what Wright is doing so he'd know whether or not it would work.
I think Janet being in this movie is a real longshot, but I agree with this. If they wanted to do it, stepping on Wright's toes is probably the least of their worries. They've had a good idea of what the Wright script is like for over a year now so if Black wanted to use one or both, it could be easily done without screwing up anything Wright had planned.