Neil and DOS both told you that you can have a single core run different ways by using Content Override. Content Override will apply the core settings you set to any game launched from a certain folder. Content = Folder. So have all your gx4000 roms in one folder and cpc in another. Load a gx4000 game and set the core settings then apply the Content Override. Do the same with cpc....launch game, set core settings, apply Content Override. How you select the Content Override is right in the image below from the link you were given (it is the sentence under the bulleted item).