If I were going to attempt to a change, I would not remove the decal but simply apply a new one on top of the old one. I think you can purchase decals that single sheets and not individual letters.
There will be a little lip at the edges but similar to what all decals have....I would not risk fouling up the paint with a heat gun or razor to make a minor correction.
It has been my experience that many of the decals are stronger than the supplier suggests and you might not need to clear coat it....not all factory decals were coated anyway.
JM2c's, Ben