Are you able to reassign "Fill selection with foreground color" (alt+backspace by default).

I'm trying to adapt using a "one-handed gaming keyboard" which doesn't have a backspace key, but I can't seem to find the fill selection with foreground shortcut in the settings. If I try to rebind alt+Backspace to any other command, there is no sort of "this key is already bound to x" response so I'm thinking you probably can't even reassign this command at all?