I've seen a few people do this kind of thing on YouTube, and was seriously thinking of following suit to restore the gold on my NES copy of "Zelda". If it works, I'd like to continue with restoring all my carts, for various systems. So far, here's the only things I know about...
1) Obviously, use non-flammable spray paint, formulated for plastics.
2) Consider sanding the carts down with a fine sandpaper.
3) Use protective tape to avoid label damage.
Any other ideas or tips on the subject? I'm all ears...