You first need to tell NifSkope where to find the textures.
File>Resource files: Set the textures.bsa here
Render>Settings: If you have extracted textures to another location, you can set that folder here.
Thats the easy part
what I see thats different is under NiMaterialProperty theres no NiSourceTexture with purple icon and path to pick the .dds file to use as texture
when I look at a file under NiTriShape I see
NiTriShape
> BSShaderPPLightingProperty
> NiMaterialProperty <------------------------ This has no source like it use to to pick a .dds texture
> BSDismemberSkinInstance
So I guess this has become much more complex now
If I change the colour of a texture or add a marking/logo or what ever to the dds it's changed for the whole world so not to unquie a
It seems it not as easy as copy the nif rename it change the textures using NiSourceTexture save it and dup the item in CS and select
the renamed nif to have a unquie item