Adrian
Its important to realize what registrations are, just pointers to various functions which you or someone else thought worked well for a song. Just like styles, some choices might be to your liking, some might not, and some might just be terrible. And of course, because they are only pointers to items, they only work perfectly if the same items exist on your keyboard, are stored in the same place, and settings are the same, otherwise they will not find the correct set up. Hence the need for tweaks. When you buy commercial registrations, these things should be for the correct keyboard, and work, but not necessarily if you download someone else's. And I always think of these song setups like decorating a room in your house - would you want to use the exactly same furniture, colors, fabrics etc as someone else?
Mike