hi DerrangedMusketeer,
this mod should be relatively easy.
Dismounted NE BG is avaliable to all the NE factions already in the EDU file, and all the unit cards are in place. all you need to do is to add a line in the export_descr_building.txt file, and use the mod switch to launch on your mod folder.
I'm at work at the moment so I can't show you exectly how you do it but all you need to do is to copy & paste the line with "unit pool peasants" and change "peasants" to "Dismounted NE Bodygard" (or early/late bodygard) at desired castle level. I can't remember whether the explaination of the numbers are the begining of the file or not, can't check this as i'm at work now.

if you need to add to factions other then NE, then have to wait someone find out how to mod the model files.

good luck.