(1312779) Shader Graph: Unable to control keyword exposure in Material Inspector

The issue I see are two issues working in tandem:

1312779: No UI to set Exposed parameter of a keywork despite being mentioned in the documentation
1312776: keyword control disappears from Material Inspector when its reference is overridden

Solving the first one would solve the second one, but I opened two issues anyway just for tracking purpose.

So my second issue is a duplicate of 1306820:

The first issue is now on the tracker: