Take a look at this thread I found on TWC. The tutorial has another link (first one)which further defines the steps on adding units.
http://www.twcenter.net/forums/showt...kingdoms+units
Also I found this here, although it is for adding a complete faction, however it may also outline the tasks or principal for adding extra units from Kingdoms.
https://forums.totalwar.org/vb/showt...kingdoms+units
Otherwise have a good look around the "Learn to Mod" section in here, there is bound to be something of good use to you.
Hope this helps.
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