Hello, I have been gone for a while, but I promised that I would upload an addon where the rebels are unlocked for Medieval 2, enjoy!
Just extract the descr_strat.txt file into D:\Steam\steamapps\common\Medieval II Total War\data\world\maps\campaign\imperial_campaign, or wherever your Medieval 2 install location is.
You should not use this addon with the main mod, this is a separate addon.