Just tested it now, and it's working here. There might have been an update to the file, so I would suggest deleting it before starting the game (this will obviously reset all your bindings).
Start the game so the files is generated, exit and open the file.
Make sure you only edit the correct portion of the file, as highlighted here for hipfire sensitivity:
Look for the "PCMouse" section and only edit the "vert" and "horz" lines: