Is it legal to upload a moddet version of the game like BHX did?

No Mods Are Not Aloud In Speedrunning Because Its Unfair To Others

Yh but the Mods dont actually affect the gameplay they just add features

Look at the rules. It says "only modifications allowed is the "PreEnabled FPS and SPEED" and the "updated version " in https://www.speedrun.com/rerun/resources"