Hmmmm... I didn't realize we could charge for it, I was thinking we'd offer it for free. Thanks for that idea Kein, I'll think about it over the weekend
Such a patch would indeed be the best way out of this PR problem. Only you can say if it would be economically feasible though.
Incompatible savegames wouldn't be much of a problem IMHO. Just add another pop-up during installation to make sure the user understands what's going on. And while you're at it offer to move the old savegames to another place, etc.
What you (pl.) possibly could successfully communicate is that you would like to limit the patch to registered users. A list of registered users is valuable for people who want to sell another RPG.
Of course I don't know what kind of infrastructure would be required for this.
