It has been ruled that affixing a control sheet to a joystick is legal here: https://vexforum.com/t/answered-control-sheet-affixed-to-joystick/42128/1
Is it legal to utilize the threaded holes on the joystick to attach the partner joystick? To be clear, both the main and partner joystick would not be permanently physically modified, and would not be modified electrically in any way. Attached are photos of what I am describing (all parts are vex parts if that matters):
