If I recall correctly there was a “workshop” article about this several years back in MR. As I remember the author (Jeff Wilson?) used Pinesol to strip off the decals. I have tried this method on some Athearn locomotives and it worked, although it removed some paint as well. If you’re careful it should work fine, just let some of the pinesol saturate the decal for a bit before prodding it off with a cotton swab.