You would need modify the code base for serious mod. If SPMBT devlopers would make open API for AI, armor, weapon and terrain effects, so that user-compiled dll could be plugged in, like in the Civilization 4 it would be possible. Otherwise I don't see much possiblities for mod.
Some more work was done by a few of us, but as of now its in limbo
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"The enemy has demanded surrender at discretion, otherwise, the garrison are to be put to the sword...if the fort is taken.
I have answered their demand with a cannon shot, and our flag still waves proudly over the wall.
I shall never surrender or retreat."
Lt. Col. William Barrett Travis- The Alamo-1836