I still don't know how to transition between versions without losing progress. Can someone please advise?
New versions aren't save game compatible. You can import your character and then use the Cheat Menu to boost yourself to where you were at.
Even with Savegame editor? Also, is there a way to cheat myself back into the castles I owned?
You can attempt to use the Save Game Editor. Remember to have both of the versions of the mod installed when you do.
You can use Cheats to auto siege and take fiefs. The options are in the town and castle menu when you have cheats active.