All content should be in INI-style format in a .cfg file. These files are loaded into the game to generate all of the content in the game.

Some of the files support local overrides. You can add a local override by creating a .cfg file with the same name in your user data directory.

On Windows this should be:

C:\Users\<username>\AppData\Roaming\Godot\app_userdata\Locked\<filename>

This allows you to iterate on ideas in a way that can be easily integrated back into the game. Just upload the new file to Github after you've made your tweaks.