Can I just object to the naming of Privates as Privates?
Thats a modern designation not a medieval one. Plus its not proper Imperial Legion designation either.
Please if your going to make the effort to do something as amazing and cool as this please do it right. http://www.uesp.net/wiki/Main_Page
http://www.uesp.net/wiki/Morrowind:Imperial_Legion
The above is a link to the ranks of the lower parts of the Imperial Legion below the Imperial Knights and Blades; proper designations that dont appear to have been changed between MW and OB.
As petrus points out, the names come from Guard_Names.csv in Wrye Bash. You can either deactivate that, or copy/rename/edit it to names/ranks that you like. The logic of Guard Names runs like:
1) Town guards are (mostly) not members of the imperial legion, although they enforce imperial law. (I'm not sure if IC guards are members of the IL either. They're clearly NOT regular soldiers, but rather are town guards.)
2) There's some variations between towns in how ranks are named.
3) Likewise, imperial legion soldiers who have road routes and and wander the forest have some special titles ("Roadsman").
The term private http://en.wikipedia.org/wiki/Private_(rank), so it's not that modern. As for Morrowind ranks, those are designed for the player to advance in (e.g. note that one of the ranks is "Agent" which presumably would be an unusual rank for a soldier to have. And as petrus points out, no spears.