I don't have direct experience with that situation, but I expect that everything would go okay, EXCEPT for any pre-defined codesets that had changed between the two versions. So, for instance, if you were using a predefined codeset for X10 (Aux 183) on your old-firmware MX-500, and you cloned it into a newer MX-500 where it is known that the layout for Aux 183 changed around, then your newer remote would have different behavior. But I think all the learned codes would move over during the clone just fine. Macros would probably need adjusting if they depended on a changed codeset.