My apology for being nosy. But I got bored at work.
@G228msport, I heard that Shelly BMW pretty cool about mods car.
I always bring my F10 528i and F15 35i to New Century BMW.
Both car running JB4 and to answer @nalinax question, I do have catless downpipe on my F10 and the JB4 clear the CEL.
I was running Stage 1 on my F10 until I had a downpipe which throws CEL.
When I was running Stage 1, I always uninstall it whenever I bring the car to the dealer since it was very easy. But since the Stage 2 is connected to the DME, it is a bit hard to take it off. Fortunately with the Stage 2, you can switch the map to map 0 and it becomes undetected.
As for the recorded MAX boost. How often do you drive your car with Max boost under normal condition? Unless if you redline the engine all the time, then yes, you will record the Max boost +3psi gain from the tune.
But, as G228msport mentioned, they will not look into your engine log for your AC problem, because it is not relevant.
Piggyback is actually the safest and most reliable tune, because you are still relying on the stock ECU for the failsafe. Unlike the flashed tune, a mistake on the tune, it will fry the whole car and will most likely voiding the warranty (unless if you go with DINAN, which is overrated). Also, with piggyback, once you are done with it, you can always resell it or use it on another car with the same motor.
For the installation, on the N20 tunes, that are 4 pairs of connector and 4 cables. On the Stage 1, you only use the brown cable connector pair, the rainbow color connector pair, and the purple cable connector pair. The blue cable connector pair is only used if you have the pneumatic boost solenoid.
While on the Stage 2, you don't use the purple cable connector pair and same scenario on the blue cable connector pair. Then you have to connect the red wire to the positive and black to the ground. The rest of the 2 wires (green and brown) need to be connected to the CAN system.
I hope I can help fellow members to answer some of the questions.