I want to be able to time my in wall air conditioner. Can I update the controller?
How I hacked my window unit for IOT control:

This (admittedly slightly janky) setup allows me to easily undo the modification in case I need warranty service or I'm going to resell it. I didn't have to use a soldering iron or spend all weekend trying to hack into the control board; I just hijacked the code the AC already runs by lying to the program's inputs.

My window AC had a thick solid copper "wire" centrally behind the intake filter that connected to the thermostat. It's usually placed there so as to sense the temp of the incoming room air more than the outgoing cold air. If that sensor gets hot enough, the AC turns on. This is typical and common. You might have to remove the plastic face of the unit to get to the probe, but you don't have to deeply disassemble the whole thing.

I first cranked the AC thermostat up to 85F, making so that it almost never comes on, unless it gets really hot in the room.

I then taped a small heater to the AC's exposed copper temp probe. you can use a strip from electric socks, a USB drink warmer, or if handy with electronics, use a simple ~150 ohm resistor to short a 5v power supply. You don't need/want more than 1/4 watt of heat. 

Wrap the heater and probe tightly with gorilla tape. You should be able to smush it all in-place and keep the cover as expected. The thermostat is almost useless at this point, so it doesn't even need to stay in the air flow, you can tuck it all to the side if needed for the fit.

You might tell where this is going.

To turn on the AC, my smart home system applies 5v to the heater from an arduino-like box. This raises the temp on the sensor above 85 and turns on the compressor.

My smart home uses an external temp sensor to monitor the temp and tell probe heater when to turn on and off. The AC on/off state will be the opposite of the small heater on/off state. 

This mod isn't for everyone, but it's probably more approachable for many than splicing into the AC's wiring or trying to clone an IR remote control.