Im no expert here guys, but I don't think this is a good idea.
I come from many years of flying collective pitch RC helicopters and good set of blades are usually balanced and weighted from the factory. A bad set of blades would cause the helicopter's aerodynamics to become unpredictable and the helli would bounce up and down in a hover. Putting any type of uneven
weight on the blades is like flying with a VW on the wing.
I seriously doubt there is any issue here. This isnt a coating - it's actually penetrating and dying the plastic. It's also consistently applied, and has to weigh almost nothing compared to the props themselves.