I've got a subset of the bonus powers unlocked, but I've been paranoid about picking one. If I regret my decision later, I'm not sure what I can do about it.
For instance, picking a power appears to cost 4,000 credits. If I change my mind, will I have to pay 4,000 credits again to unlock another? If I want to switch back to the first power, do I have to pay the 4,000 again, or is paying it once per-power sufficient?
Also, what happens to any level-up points I sink into a given bonus power if I switch? Do I get those points back, or are they applied to the new power in the same way they were applied to the old?