I am just a hobby builder, so my methods are not for production. I'm sure they would have to be adapted in some way for production, if they would work at all.
I've found that anything that adds weight to blades effects their spin, slowing it down. The thinner the coating, the smaller the effect. I have coated and fished chatterbait blades with black Shrapies, topcoated with Createx transparent base and then Rustoleum x2 Gloss Clear Acrylic. I can even paint my spinnerbaits and blades, primed with self etching primer, with Createx paints and then topcoat with the Rustoleum, and it holds up just fine
For me the most durable blade coating has been finger nail polish. It is hard and tough, and doesn't seem to be affected by temperature changes in the blade's metal.
I've tried powder coat, and it made the spinnerbait blades spin more slowly, but it seems to change the thump on chatterbait blades in a good way.