It's not mystical at all and if you Google it plenty of people have had warranty refused. Anything you change is detectable if you know where to look but that's IF you know where to look. It's the fact some companies and people say it can't be detected when it actually can.
Please stop saying they're detectable and actually link some proof. I'm genuinely interested.
I don't think anyone needs to prove anything. The point is, this forum is for people to offer advice and experience on matters relating to what we all have - Golfs. You can take the advice or not. The link I shared from a previous clearly shows the VW information provided to dealers. Whether this happens in real life no doubt will be case by case.
And to be fair, the thread was about an exhaust and started by someone else so you should respect that and start a new thread re detectable tuning if you are really that interested.