all the textures are saved as hmp skins, and the last 4 ones are assigned as the 4 material skins on terrain creation (material bmap pointers to entity skins).
I just tried to modify the full texture atlas. they are tga textures. if it will work fine, I think I replace the old dll with yours.
as I remember performance is slightly better when dds textures are used, but they can be converted for the game. currently I have a secondary option to save a terrain texture package (and a terrain lighmap texture) for each level as a set of separate tga files.