Transferring Textures

I’ve been working with the vanilla models with Milkshape – adding helmets increasing the variety etc. The problem is I’m only able to add parts for which there is already a texture for that unit type. For example I can only add helmets to units from the ln_lmail_hmail file that already have textures there. Is there a way to transfer textures so that I can use helmets from the en_lmail_hmail file or ln_3qplate_halfplate file with their vanilla textures on units from the ln_lmail_hmail file?