Controller modification legality

Starting to think for next season and am wondering what rules (if any) their are for modifying a v5 controller, what I’m wondering if you can do is 3D print levers so that buttons that are harder to push can be pushed easier and by different fingers.

You can 3D print levers or objects that make it easier to use, but not modify it’s circuitry, or functionality


There are actually files for this type of design somewhere. (Thingiverse?) It’s perfectly legal.