I imagine that it is only necessary to do 3 things:
- Preserve textures format (BMP).
- Preserve the size of the textures (each image has a specific size).
- Possibly, keep the name of the textures. That is, replace the new textures with the existing ones.
I guess every texture (image) should draw a pattern that can be repeated. I can be wrong, but I think these textures can deform, stretch, to fill a larger area.
Whenever you manipulate original files, make a backup before.
The simplest is to copy an entire folder of a specific texture style, and manipulate its images, preserving the size and format. Finally, change the name of the folder, with the name chosen for the texture.
I don’t know if it’s possible to create new style folders. All folders have the same number of images and the same names. In theory it should be possible to add new entire texture folders.