[thejeff]

Essentially no. The independent defenders stay put and do not change, other than being killed.

That said there are a couple of things that can change them. Most commonly, independent provinces can get events. If they get an independent attack (barbarians or knights or whatever) those will join with the original defenders.

More rarely, but neat and dangerous enough to mention, indy commanders can be generated with magic items. On occasion, one of those items is a Soul Contract. If you see an indy province with Devils, be careful. Most likely he's been getting one devil a turn since the start of the game.