Changes to War demand might present an interesting option - probably should be reserved for if you can get such a unit to a capital city. 

Increasing cultural influence might be trickier. 

Training rebels seems dubious to me as a good ability, but, hiring a militia from an independent faction might be workable. 

There's probably already a function for disrupting trade - you destroy or damage the district working a luxury or good. 

meh to stealing science / production / money - but maybe - converting briefly a luxury or good.