Where does Glyphs store the list of nice names? And what about the list of combinations used to make component characters (the alias.dat for Glyphs)? I’ve run into trouble with oddball characters, for example, in FontLab I use uni030c.alt for the alternate Czech form of Caron, but I have to build ď and ľ manually in Glyphs.
First, call it “dcaron.loclCSY”. This ensures that Glyphs adds it to the locl feature. It then should pick up the components. You will need to change the alternate component.
You can browse the glyph data in the Window > Glyph Info.
Or, if you are interested in the detail go to: