When adding for instance, E.ss01, perhaps the new glyph could have the E instead of blank spot?

You mean automatically add a component of “E” or just showing the gray proxy glyph?

Automatically adding a component. Or just a copy of the outline.

Both methods are already implemented. You can use Font > Add Glyphs and the recipe E=E.ss01 to add E as component to E.ss01.

Or you duplicate E (or any number of glyphs), and rename ‘.001’ to ‘.ss01’ with Edit > Find > Find and Replace in the resulting glyphs, and you have a copy of the outlines in the new glyphs.

this recipe approach is really nice!