Here are the topics that could be useful:
https://forums.totalwar.org/vb/showthread.php?t=13155
https://forums.totalwar.org/vb/showthread.php?t=32132
https://forums.totalwar.org/vb/showthread.php?t=30803

It's far from being easy to modify the campaign map. Some smaller task could be achieved by simple copy & paste but adding a province is quite tough (there's a limit also).
Removing one is a lot easier...

Alex