Okay, here is the idea... and it will only work if the enemy is equipped with the particular armour set and "shield" I am about to tell you about. But that is okay. We don't want to be chopping arms off constantly in every fight... it should be a special occassion.
Okay, so I make a certain troop wear this modified armour.
It is modified in the sense that half an arm is missing, from the elbow. It's the shield arm. We will also have to make an invisible glove for the troop to wear... his real
shield arm below the elbow will have to be completely invisible to the player.
I then make a "false arm" like this:
This arm will be treated as a shield - it will have all the attributes of a shield, will be entered into the module system as a shield (with low hit points), and will be raised in battle like a shield (it is positioned exactly where an arm holding up a shield would go) - and it will have to be converted to .md3 format at some point, because all shields are .md3.
In battle, the enemy wearing the armless armour, the invisible glove, and the "false arm shield" (bear with me here) will raise the false arm as if trying to defend himself. It will have to be positioned exactly in Wings or BRFedit to meet up with the movements of the "armless armour" as much as possible.
Like this, though of course the rest of the arm will be more bent and closer in while in the game:
Hopefully we can put the hand on the right way up as well.
When the player hits the "shield" it will react as a weak shield does - by breaking and twirling off into the grass, leaving the enemy appearing to have one arm... like so:
Here is an artist's impression of how this would look in the game with a sword cut doing the damage...