Thanks!
For filling in small narrow areas like lettering I start by making sure I have a nice clear coat over the gold metallic. I use a gloss clear acrylic. Then I just smash paint down in the letters and wipe across the surface with a damp towel. The black is flat acrylic so just water to wipe away from the surface.
For the larger areas that get blue paint I’ll use a syringe to fill it in.