I there a solvent that will remove powdered paint?
Cadman over at TU uses something called "Parks" paint remover, but I tried looking it up and it says dis-continued. If you find it - and try it he says leave it over night take it out wash it off with warm water and Dawn detergent then make sure it's completely dry!!!!!!!
Myself I usually just melt them down again, they will smoke a little but I do that outside.
If you only have a "FEW" you can reheat them and using a heavy cloth wipe it off. If you haven't cured them yet you should be able to just scrape it off.