The 3M stuff is made to remove VINYL 'decal' which is a sticker not a true decal. It's also intended for sticker on TOP of the paint, not under a clearcoat. Big differences there. True decal is a layer of PAINT or INK made to come loose all at once from a water loosened backing, it is specialized to come loose while together, and adheres simply by being stuck by capillary action. Shooting clear over it makes it part of the base paint itself when the solvents go through the decal to lock it to the lower paint color.
I have removed vinyl decal on top of paint with no clear all day long with virtually no damage other than the paint faded marking where it was. You need no special tools for that.
Luck with whatever you do there..........people will make you think the 3M stuff can do anything to sell product but like everything else the details of the work matter greatly as to whether it works or not.