First you should decompile your battle.lgp (using LGPTools, Highwind or Aali's UNLGP). Then you must locate the battle location you want to modify. I guess using Biturn would be a pretty good way of previewing them. Then find it's asociated textures. The textures of a battle model whose name is XXaa (where XX are the two first letters of the filename) must be between XXac and XXal in a lexicographically ordered list. You should replace these textures by whatever you want (of course you should convert them to TEX files). You could use Kimera for doing. That way you can also preview the result.
Sweet, i'm looking into it right now, i didn't quite realize how bad the quality of the textures actually is until now.
Providing everything works out the way it should, i'll put up a goal of finishing the first bombing mission areas, when/if that ever gets done (motivation is a b*tch), we'll see if i'm still up for it, perhaps i can at least spark some interest.
Edit: Followed what you said, so far so good, don't know how to replace it in Kimera though, the buttons and the dropdown is there and all but they do nothing.