Use TRS jack as Mono + 5V power input

Question

I'm trying to change this guitar wireless transmitter so that the audio input jack also becomes a charging/power source.

The charger will be a separate box with "stereo" input socket.

Currently the mono jack (see OUT/GND pin) gets Mono audio from guitar and the micro USB port powers and charges the battery (see BAT +/- pin).

I have two questions:

1. If I use the ring part of the TRS for power can I share the ground with the audio one?
2. When plugging in, tip of the jack will also temporarily connect with ring sleeve socket connector. So can I use a Zener diode (maybe around 2 volts??) to prevent power going into the Mono audio input

There is a wireless transmitter on the market called NUX B5RC that uses this way.