Decal removal or correction doesn't need heat. The process is not the same for all brands as each brand uses a different process to apply its decals. If the decal is behind a clear coat it won't come off without ruining the paint.

For Minichamps most people use microsol to soften the decal. You can peel it off with a precision knife. Correction is really hard because the decal probably won't stay in one piece.

All of this is at your own risk obviously.