I think this is actually really necessary and here I will show you my ideas.
First of all, add 4 new keybindings to the settings called Button1, Button2, Button3 and Button4. None of them do directly anything to the game but will do if we add something.
Second, in Game Settings, add a new option called "Control Settings". Inside it, we have just all the keys possible and the possibility to change these things:
Enable/Disable it, if we want to make it don't show on settings if we don't use it. Rename the key names, even those who are the default. Set a default key value for each player and also the button in case if you're using a gamepad.
Also in Game Settings, add an option to select if we want that default keys we set are replaced at the start of a new game when playing it, overriding the master one at the title, but not removing it.
And lastly, allow sprites to have a command input called "Mouse Off"
