Suffixer is a little RoboFont extension for editing glyph name suffixes. It can append a suffix to the names of selected glyphs, or replace an existing suffix with a new one (or none) in selected glyphs or the whole font.
Suffixer lives in the Font menu of RoboFont under the heading Change Suffixes..., or with the shortcut Cmd+Alt+Shift+S. It comes with a list of suffix presets modeled after OpenType feature names; you can of course also use custom suffixes, which will be saved to the extension preferences and subsequently included in the presets list.
Some things about renaming glyphs, and a word of caution: If you rename a glyph from RoboFont’s main interface, you are asked to confirm that the glyph should also be renamed in groups, in kerning, and with regard to components. Suffixer has all these options on by default, which means it should not break things like composites or kerning. It also globally assigns auto unicodes in the end (which is relevant if you are using it to add or remove suffixes). When trying to rename a glyph to a name that’s already taken by an existing glyph, the latter will be renamed to [its present name].copy_1 (or if that is taken, .copy_2 and so forth). So nothing should break – but always use caution (and backup copies).