It depends on how much clear in there. You can't go wrong to just wet sand the thing with 600 and see if you can cut it flat without cutting thru the clear. Often the clear is very thick. But if you do cut thru, then yes you will need to remove them, and if you do, you will then probably be hitting plastic, that will change everything and you will need to apply some plastic primer or adhesion promotor depending on how much you hit. It's that, or you sand it with 320 or so and prime a few coats to build it up so you don't have to remove the decals. But really, the right way would be to remove the decals unless you can sand it real easy with the 600 and not cut thru. Honestly, if you can do that, paint that sucker and leave the decals there, they aren't going to hurt a thing and it would save you a LOT of work.