Go to X:\Program Files\SEGA\Medieval II Total War\data\world\maps\campaign\imperial_campaign/descr_mercenaries.txt

(make backup before changing or opening)

Well I tried something and I put king henry as avaliable mercs in the british region and it worked any one has anymore idea??
I think ill check if I can make the king availabe to recruit in custom battle and that will be much cooler then a regular generl...