This mod will allow you to take COS (with CTCSS) out of the UV-5R.
It will make the center pin of the bigger mic plug go to ground with
receive activity. Use this to feed an Allstar interface for example.
Set the volume to halfway. Use a silver sharpie to repeat the settings.

Take the battery off.

You need a T8 Torx.

Use an antenna wrench (or the volume knob has one!)

Take off the nuts.

Take off the belt clip T8s- mind the spring! It fell under your desk.

Unscrew lower T8s, then pry the radio out of the case.

Then that Philips screw.

Mind the fragile speaker wires.

The general area of interest.

An NPN transistor-Emitter to ground.

Flat side down.

A small 1000-2200 ohm to the base.

A thin wire from the base resistor.

Heat shrink tubing.

Gently bend.

Tack solder the base resistor lead to the 8-pin IC.

Collector wire straight to that solder pad.

Mind the gasket when reassembling.