How do you add category extentions?

You need to request "Category extensions" to the site, just like you do to any other game. In the game request you should state that you are requesting category extensions for a certain game.

There are several conditions though for the game, for the site staff to accept category extensions for it. More information here: https://www.speedrun.com/The_Site/thread/mcxme

Thank you for the feedback, but I did not request because game isn't popular enough.