Coming back to this. Let me provide a simpler scenario:
I have a file with .ss01 glyphs. These are single-storey /a glyphs, so the feature description is “Single-storey a”.
In the italic, I want to switch this. So the default a is single-storey and the ss01 contains the double-storey a. The feature description should thus be “Double-storey a”.
I would like simply to change the feature description, not the feature code.
I realise this should probably be unified in a font family, so that the feature description can be displayed correctly when selecting a body of text that contains both roman and italic. But still, is this possible in Glyphs?