Go to
SEGA\Medieval II Total War\mods\kingdoms_grand_campaign_mod\data\world\maps\base open descr_sound_music_types.txt with Notepad. Let's say you want to move Spain to the Northern European type. You cut and paste it from one type to another. It should look like this:
Then, in the
SEGA\Medieval II Total War\mods\kingdoms_grand_campaign_mod\data\sounds folder delete the events.dat, event.idx, music.dat, and music.idx files (you might want to make a back up first, just in case).
P.S. Next time, try to use TWC's search engine in the Mod Workshop.