Well I think the market is telling you that it's not a good idea. If people will only accept it with a watermark or some kind of distinguishing characteristic then you've defeated the purpose of the new label. What they're saying is that yes they wouldn't mind a new label, but no you can't make it exactly like the original. Then you're stuck making labels that are similar to the original and I think that's where some people might lose interest in an impulse purchase.

BUT....you could do good business with retro game shops, maybe. Just something to throw on average titles to make them look better. Or maybe people will buy the stickers to collect.