From your description of your particular problem, it sounds to me like a creating an entirely new module will be your best option.

To eventually be able to replace the errant module, you might want to entertain a sub-name space that can be, at first, optionally "used/required", then later as the old interface is depricated, becomes the default. This is somewhat like the idea of wrappers, but possibly using inheritance to 'fix' the broken interface with a new version, but leaving the old one accessible as is for now...

-Scott