I made this quickly so it's not the most refined but yeah it works so who cares!
To start, install the repository through .zip or clone it and then change your config.json to have the "robloxVersionsPath" field be your Roblox versions directory, also feel free to add to the blacklist in the JSON file if you want some fonts not to be changed!
Save that and then drop the font you would like to use in the font directory and rename it to font.ttf (make sure you have the file extension as .ttf)
Now go ahead and run the Python script (IMPORTANT: make sure you have Roblox closed otherwise it'll break it and you'll have to reinstall, trust me I accidentally did it to myself.)
Your script should end with
everything should be that font now!
however, make sure that before it says that you see something along the lines of this:
|-REMOVING zekton_rg.ttf FROM DIRECTORY C:\Users\<USER>\AppData\Local\Roblox\Versions\version-24872f7beace4d0a\content\fonts
|-> File deleted successfully
If all of that is working then go ahead and start up Roblox, now everything should be that font now!
If you run into any errors or bugs then it's probably something wrong with your JSON format so make sure to double-check that!