I just buy new plugs. They are cheap. I have never had a plug fail but I generally put in a new pair every couple years. Using NGK BPR7ES made in Japan.
Aircraftspruce.com sells aviation approved blasting grit that does a great job on plugs. Champion part number 91893. It tends not to leave leftovers particles at the bottom of the insulator.If you sandblast with plastic grid you can soften the Surface. A corn of 50 Mikrometers is often used in dental laboratorys.