I just upgraded to 5.6.02 from 5.5.1.2 and immediately noticed the changes in the C5 libraries/models. It seems to me that the new, best, way to overwrite core functionality is to create new files in the same places as before and extend the new library/model (concrete5_library/model_foo_bar) and add/overwrite methods that way.

Is this the, intended, overwrite procedure?

I will say right off the bat, that if this is the way you guys are intending to go, I love it. Had this methodology been in place before now, my upgrade would have been incredibly smooth.