In post #2, you answered the bit about a plug in module, Andrew, but not the bit about visibility re servicing.
Is the module visible to dealers please ?
Also, is there any "smoke" under load ?
The plug in module would have to be unplugged before you took it to the dealers. It's prior fitment is presumed to be untraceable because the signals sent by the ECU to the common rail and the boost sensor are intercepted and modified by the box and then sent on their rightful way. These modified signals are not fed back to the ECU for it to know that the signals were altered, nor do the receiving sensors have any memory of signals they have received.
That is the way I think everything happens with a 2 channel tuning box, maybe Andrew can confirm?
I'm also presuming that the DPF would capture any "smoke" (particulates) under load and if there is masses more particulate matter produced then you'd have more regens.