You can override only entire elements, not skins/components/individual Building Materials.
Those clips do the same: if you look closely you will see that all Doors, Windows and Curtain Walls are glass.
In the attached image you can find the GO Rule that overrides all Doors, Windows, Corner Windows, Skylight, Curtain Walls with the "Glass - Blue" Surface. (Curtain Walls were used to model many of the large complex Window surfaces of the building).
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2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac28