Most stickers are fairly easy to get off with little to no harm to the label. If you are very careful about it.
It totally depends on what kind of game cartridge you're working with though. If it's a NES cart, luckily the labels are laminated. So as long as there's no spots where the laminate is worn down or gouged. It should be pretty easy to remove a sticker with some rubbing alcohol. For extra sticky glue residue I always use a little bit of vegetable oil. Rub it on and the glue balls up and wipes off. You have to be a bit careful at the edge of the label though. Because where the laminate ends the paper label is exposed. So it's possible to soak up excess alcohol/oil and cause permanent discoloration.
Unfortunately Sega Genesis and most other cart based games don't have laminated labels. So that renders alcohol unusable, as it will destroy the ink on the label. Vegetable oil is
okay as long as you stay away from the edge of the label. Use a very, very soft cloth. As anything even a bit rough will start to rub off the ink.
I've had great success with some pretty bad examples of stupid sticker placement.
So anyway, uh end of lecture.
