I'm not a modder, but perhaps someone else can help you if this is incorrect. You may already know that you can DL the game Dbase here:viewtopic.php?f=340&t=35005
The CW2_DB_Models_v9s.xls file contains the General's list starting on line 243. Starting with Column CA, special abilities are listed for each General. All of the abilities in the game are there, but you would have to hunt for each one from a General that has it. So if you want someone to have the Fast Mover trait like Jackson has, then I suppose you would add $abiFast_Move in one of these ability columns for your chosen General.
I'm not sure how to add your own Generals, as you would need a graphic icon for each one. You might have to do something with the Unit file for this. Hope this is of help.
P.S. You would of course have to make these changes to the actual game files for them to take effect. I believe that the Unit file also has the General's skill data (Strat/Off/Def) that you could alter.
I'm the 51st shade of gray. Eat, pray, Charge!