I would reassign texture materials in a 3D editor, which are located in default game texture folder and labeled with original_name1.dds instead of original_name.dds. For example, in blender, you import the .NIF, rightclick on mesh, hit TAB, A, U then change in UV window, go to image menu/replace and load up your new texture. Then hitting F5, click an "assign" and tick "face textures." Then, hit TAB, hit A, go file/export/.NIF and you have it. problem is the nif is still a Bethesda mesh and I cant upload it I believe