Something like Bruce Banner turning into the Hulk. I have a model with lots of shapekeys to make different characters. I'm usin the pitchipoy rigify (or any) and i wish that when i modify the model to a desire character the rig follow the size and shape, so i don't have the need to do it manually everytime.
Not sure it's possible. Editing a rig in animation compromises the relation bone - weights. Mesh weights become wrong and the rig influences it's mesh in a wrong way.
What I've seen in such problematic, is to have two models, each with it's individual rig, and when one model morphs to take the shape of the second, they simply switch the visibility.