I see you found this already as I got notified of a new like:
With it you can make small mods, though as I noted only one such mod can be easily installed.
Godot has support to load additional pck files as well as load C# from extra dlls, so if someone adds (cough GitHub - Revolutionary-Games/Thrive: The main repository for the development of the evolution game Thrive. cough) support for mod loading in Thrive, we can have proper mod support.
Without the tool you couldn’t make any mods (except trying a different Godot engine version by replacing the executable), as this is what you get in Thrive releases (the data folder contains just some Mono files):
