if the FC is different that won't work
Incorrect. An XML export/import is expressly one way to manage radios with different flashcodes that have otherwise identical codeplugs. Trust me, I've migrate a number of 6000AN codeplugs to 6000BN using that method, and the flashcodes were quite different.
The other method is to drag/drop between codeplugs with two instances of CPS open. You can even do a top level drag of the entire codeplug. This method is easier than XML export/import because you don't have to delete the phantom crap first, like the first zone that always screws up the import of scan lists because everything is shifted one zone down.
Oh and by the way, since we're talking about cloning APX radios...more recent versions of CPS have started to be more forgiving when cloning between mismatched flashcodes. It used to be very strict and the slightest mismatch would cause cloning to fail, now you might be able to get away with cloning from a lesser capable flashcode to a more capable one, as long as the radio models are the same and there isn't a vast difference in capability. For example you can clone from a 6000 that doesn't have tone signaling or group services to a 6000 that does have those features.
End of today's lesson, boys and girls.