Since the source code is.. just there in the mod files, it's simple.

Go to your steam workshop content folder, found under "\Steam\steamapps\workshop\content\"

Then go to 1118200 for People Playground workshop items and find the folder 3550751257.

Inside here you will find the mods files and code.

Open "all.cs" in visual studio or some kind of coding program.

Press CTRL + F and put in "CategoryOverride = ModAPI.FindCategory("")," (Not the quotes around it, duh.)

And set it to replace ALL with "CategoryOverride = ModAPI.FindCategory("Glitch"),"

This sets every object and spawnable item in the mod, to be categorized into the already made Glitch category. (No idea why this wasn't done already but here you go )