Maximum output power with Vcc 5 Volt is 5dBm higher than with
a Vcc of 3.0 Volt. 27dBm equals 500mW. Gain will increase slightly
(guessed increase is 2.3dB(1.7 times power)). Together with the
software output hack you will get a lot more power. I do not have
a RF output power meter... Who does?
The modification actually consists of increasing the supply voltage
to the RF ampifier to 5 Volt. To supply 5 Volt to the RF5117 you only
need one piece of wire, and a soldering iron. Remove carefully (and
keep!) the little SMD coil (the big one) on top left of amplifier
section. Replace it in a standing position on its original left pad
(arrowed, which is the one that goes to the RF5117. Solder a wire
from the free end of the coil to the +5Volt supply.