Latest Testing Firmware now has a Gcode very easy to access on
/usr/share/griffin# python3 command_util.py
Using the current LED Gcode you can change the led, or turn it off. But the really interesting thing is that you can actually test GCODE commands directly like you could do from a printrun/pronterface.
Warning. Don't try this unless you know what you are doing, going into the firmware could damage something (unless you don't edit or delete you should be fine). So don't go there unless you know your stuff.
