I do appreciate you taking the time to document your attempt, it will surely be helpful to others in the future.
As an engineer I can also point out an alternative way to disable the signal, that will be easy to undo in case Rachio ever develops a firmware fix. Unfortunately, one would need to be comfortable with putting a blob of solder onto the board.
Between the antenna and the rest of the circuit, there are two pads, meant for a load matching resistor, which (when shorted) would effectively dump the signal into the ground, thus preventing it from being transmitted. Using a bit of solder and/or a short bit of wire, these pads can be bridged, thereby temporarily disabling the radio signal. Later on the bridge can be removed, restoring the full functionality.
I’ve highlighted the connection which would disable the signal with red:
Anyway, just wanted to propose a less permanent solution which should work just as well until manually undone. Good job again @hcornea for sharing your work, it’s definitely a more universal solution to what I’ve proposed here.
Cheers,
Gene