This analog joystick is its own module, both physically and in the firmware, so it is going to be independent from the other operations through the LCD or if there were some keypad. Nothing prevents the wires from running in the same bundle and being physically in a single pendant, but it will still be independent. This joystick does not have an Arduino to mediate the commands, so there is nowhere to put the extra ‘interpreter’ so to speak to translate a button press into some command.
I can see how a keypad for custom commands would be handy. The scrolling and clicking on the LCD is a little clumsy. I think a keypad would make a great addition but like I said it would be a separate thing. I think Armin’s approach would be a great starting point for a keypad, and it should work nicely in conjunction with this joystick.