Soda or bead blast. If you are taking them to a powdercoat shop to have them done, they will tell you what needs to be done.
Thay may do it over the annodizing.
I had a boat wakeboard tower that was powder coated black RE-powder coated in white right over the old powdercoat...no issues after 6 years with chipping or peeling anywhere. Sold the boat last year and the new owner just emailed me a week ago saying he loved it and it was all still in great shape.
it is easier to ask for forgiveness than permission