I think you'll have to wait for the unpacker, and then you should be able to just copy the files for the unit over to the faction directory that you want it to belong to, or also belong to. So you may not have English skins for example, but you should be able to see the unit.

Anyway that's how I'm guessing it could work from this in the unit file with all the descriptions at the top:

; info_pic_dir Optional. Dir to find the info pic in (instead of faction dir)
; card_pic_dir Optional. Dir to find the unit card in (instead of faction dir)

So I'm just assuming that the models for each unit are also seperated into faction directories also, just like the pictures.

Just a theory. :)