I've been checking the tutorials that can be found around here. It seems that you need to write a batch file in order to extract the textures from the game. I've 0 capacity to do that nor experience modding SR3, that's why I requested this mod. Nevertheless, after reading those tutorials I've understood (correct me if I'm wrong) that after extracting those textures, you can edit them with Photoshop, just like any other game (I've some experience modifying textures for Skryim, Dark Souls; .dds and .png file formats respectively). That's why I'm offering now my help, if needed, to create this mod.
I would just modify the textures needed, then I would reupload them again for someone else to repack the mod. That's it. If someone is willing to help me, we would create the mod together. But if that person prefers to make it on his/her own, that would be great too.
Anyway, I think it would be a cool addition for the game (to have this mod), so I hope someone is interested in this.