Are you saying it's impossible to add this feature and to not bother trying to do it myself?
Viewing post in RPG Maker MZ Input Config comments
Yeah, I don't think it is possible without rewriting a lot of stuff. Check out this: https://forums.rpgmakerweb.com/index.php?threads/mano_inputconfig-gamepad-keyboa... I think I've seen it support multiple key inputs for the same function