I just applied these to my RV-8. They went on without any issues. I can't speak to what it would take to pull them off. I would expect that any paint shop should be able to take them off in a heart beat.
 
Mine worked fine

I bought the 3" numbers from Aircraft spruce, applied them flew with them for a year then had them replaced in a different location and color by the paint shop - NO PROBLEM!

Bob Axsom

P.S. It was a quiet little thrill putting them on and standing there looking at it in its new status.