This is a little more difficult.
Everything has to be done by hand, no over writing.
I think though no expert, that you need to start with the AUM.
hand modify the modeldb which is a bit touchy make backups and check the tutorials, then modify the EDU by hand as well, Gondor militia units smith and upgrade lines only.
you will also have to add the meshes from this mod by hand as well, deleting the vanilla meshes. I am not sure about this though some one smarter should confirm.
Check posts 52 and 57 they have files there that may fit your needs. Do this first actually!!!