From what I recall, you "Can" swap rings on a Pioneer set, but my understanding is that it is not as simple just unscrewing chainring bolts and putting on new chainrings. The PM contraption gets in the way. I don't remember the details, but it's apparently a pretty complicated ordeal.

Harlan, why not look for a used SRM. I bought one of mine used. It's been solid, and was cheaper than a Stages.