Whenever I had attempted to edit/add anything to the menu.json file manually, the game would no longer be able to use the file and I’d have to start over from scratch. I saw in Changelog 1.6.5 for 1.12.2 it states the menu.json now reloads with F3+T shortcut “for easy editing manually”. Does this mean the menu.json is now capable of being edited? Could you show us an example of this being done?

You can edit the menu.json just fine, as long as you keep to the proper format. Best way of learning is to add stuff to the radial menu in-game, and see what it writes to the menu.json.