The Winterhold Exterior Ring has snow on the steps. How do you remove it? I tried substuting WinterholdWall02 texture and it was snowless in the popup box as I tried alternate textures but when I dragged the modified ring section into my cell it still had snow.

Check the option for directional material, on the base object for that static. It's likely got snow selected. Its one of the drop down boxes on the object.

I'd suggest duplicating it and editing your own version.