It's possible to add new dropdown values as well by editing "Data\Editor\Config\Stats\Enumerations.xml". I did this for my custom WeaponType. The problem is this won't necessarily work for everything, because quite a few things are hardcoded in of course.
In my case, a new WeaponType seemed to work for deltamods, but I couldn't find where you specify "this WeaponType = this animation set" for unsheathed animations, as they seem to ignore the AnimType field for those.
