Better yet, because modifying the base ULib and ULX files can cause update issues, create a folder on your server /garrysmod/addons/_anynameyouwant_/lua/modules/sh/
We never, ever recommend modifying the files/folders/adding anything to our base files.
Use the addon format for adding new stuff.
That way, if something breaks/conflicts weeks from now, you don't have to remember any changes made, you just remove anything but ulib and ulx folders and work your way back adding one at a time.