Defaults to 70. This is a heuristic that worked well with MY SPECIFIC FONT and MY SPECIFIC SVG's, but you may need to adjust it for your own use case. python replace_glyph.py font.ttf "glyph_name" ...

The fonts will be symlinked to your ~/.fonts folder from their original location—so you can organize your font collection however you please. FontyPython is free and open source, for Linux only.