On the .REG file...

50% Power Level:
00,48,00,00,00,80,A9,03,00,F0,49,02,00,32,00,08,00,00,00,00,00,00,00,00,00\

0% Power Level:
00,48,00,00,00,80,A9,03,00,F0,49,02,00,00,00,08,00,00,00,00,00,00,00,00,00\

But how to set a negative value?!

My take on a -50% would be:
00,48,00,00,00,80,A9,03,00,F0,49,02,08,32,00,08,00,00,00,00,00,00,00,00,00\

Does this make any sense?