The bolts or masks in this case, should not be left in the wheel and fully cured, becasue the powder would bridge the rim and the bolt. so when you went to zing it out it would crack the powder.
I could, put the bolts in, blast, clean, apply powder, then carefully remove the bolts then put the rim in the oven.
It seems much faster and easier maybe to just turn the air pressure to 15psi, shoot a steady stream of air from a blower and draw a line around the tire side of the rim, blowing off the powder in the bolt holes and leaving a line of no powder around the wheel lip only the tire mounter will ever see.
I will have to order some from McMasterCarr and give it a shot though. Just need to find the thread pitch and size now. :number1