You can use liquid paint over powder. Instead of doing the whole frame I suggest adding some sort of accent.
I don't think any special process needs to take place for power coat vs. regular paint. Scuff the surface with 400 grit sandpaper, mask and spray. Oh, add a couple of degreasing steps as well. Best paint to use is automotive paint. You might want to search out posts by Dr. Deltron for tons of tips on painting frames.
Good luck.