Yes, you can power save Pokemon and sell them. I remember a mod posting once and ended a disagreement about this. They said it was okay because it wasn't animal crossing being power saved.
I don't believe it's against the rules, considering many people here use "hacks" to breed their pokemon quicker or level them up to 100 in 0.2 seconds. Like above, I believe it's okay as long as you aren't hacking animal crossing.