So after breadboarding, I'm seeing the speaker output is just way too dim for the main LED. It doesn't even light the whole blade. So I am going with the main green die off the board's LED (-) through the TIP42, and the speaker (-) for the amber flicker / red flash on clash. It actually looks pretty good. I also replaced the stock overly-sensitive swing sensor with these and put 2 at 90deg (2-axis setup) SW-200D motion sensor

In the end, and answering my own request, it seems the following works (in software anyway) to reverse the stock LED signal behavior for a flash-on-clash effect (turning an off-state into on-state). The switch in the schematic representing the the POSITIVE leg of the Hasbro board's stock LED.
Screen Shot 2017-04-22 at 5.56.17 PM.jpgScreen Shot 2017-04-22 at 6.06.32 PM.jpg