Button names can also be of the form #nnn if the device name has been prepended with a # when it was specified to <id>.
Also see "Changing Keyboard mappings" in
the International Issues page.
Note that any time you're unmapping keywords you run the risk of leaving DMDX with no valid inputs and if you try and gather an RT under those circumstances there's a good chance you'll lock DMDX up because it can't advance to the next item (DMDX isn't of course locked up but it sure isn't paying attention to you, it is however easily terminated with the task manager). Under these circumstances DMDX's safe mode is your friend as it tells DMDX to constantly poll for the ESC key so you can abort an item under almost all circumstances. It used to be the case that having safe mode active while gathering RTs could lead to some extra variability in RT data however these days CPUs are so fast this is moot.