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You need Nifskope.

1. Ultimate Solitude SSE:
Install SStonefloor01 and SStonefloor01_n  textures.

2. Skyrim 2017 Textures by Pfuscher:
Install Smoss01 and Smoss01_n textures.

3. Skyrim 2017 Textures by Pfuscher:
Rename SStonefloor01 and SStonefloor01_n from Pfuscher's pack to something else, like "SStonefloor02x", and I suggest installing it in Textures>Architecture>Solitude.

4. Get smuseleum.nif somehow,  you can extract it from the Skyrim.bsa using BSA Extractor.  It is in Meshes>Architecture>Solitude.  I have a version of the mesh that fixes the rocks on the opposite side of the building but I can't remember where I got it, it is on Nexus SE somewhere.

5. Open smuseleum.nif with Nifskope and left-click the arrow on "0 BS fade Node" (top left window) then "34 Ni-Node" then "35 NiTrishape" then
"37 BSLightingShaderProperty" then select 27BSShaderTextureSet.

You will see the textures on the bottom left when you left click on 27BSShaderTextureSet, right click on the first texture's field and select "change".

Then you need to navigate to the location of the texture you renamed from Pfuscher's pack and select it.  Repeat this process for the _n texture, the normal map. 

Sounds complicated but it is super easy.