This Glyphs app filter replaces glyphs for another one in the font. Can be useful to replace glyphs for a demo version of a font.

Use it as a custom paramenter in an instance or in a .glyphsproject file.

Property: Filter 
Value: Obfuscator; char:.notdef; include:A,B,C;

After char: you can define the glyph name you want to use as a replacement. If char: is not declared it will use the .notdef glyph. include: is what glyphs you want to replace. Also, instead of include: you can use exclude: to apply the filter to all the glyphs in the font excepting the listd ones.

If it is used via the menu Filter>Obfuscator it will replace the selected glyphs for the .notdef glyph.

Download the plugin, open it and restart glyphs. For better update handling install the script via the Window > Plugin Manager inside Glyphs App.

If this plugin is helpful for you, maybe you can consider making a donation ;)