Final Fantasy Hacktics

I have PSP version of game and I already know how to change sprites & portraits for formation screen in game using the UNIT and WLDFACE .bins and ShishiSprite Editor for the Battle / Events. But i miss changing some sprites that doesn't show up like Luso's, Balthier's, and i wonder if there is empty Sprite Slots as there is Portraits cause i wanted to create Characters without having to delete a existing one. Tips? Guides? Help? Please ^_^  !!