I've played a few missions so far, and have gotten a handful of skill upgrade points. As I've purchased new skills, I've noticed that you can "sell" skills that you've chosen and get your upgrade points back. Is there any limit to this? Do you at some point need to stick with your decisions, or can you freely exchange your skills forever?
As far as I can tell you can move points around freely, even ones you bought before. I don't think there's any sort of penalty for it either.