Oh...and the screw/nut is off the turbo housing. Without knowing where it is or getting a good look at the turbo, which is almost impossible without moving stuff out of the way, I couldn't see a screw...unless it is on the back or underside of the turbo

 

He is talking about tightening the wastegate preload on the actuator arm....

 

Is there a thread on this? Have people done this before? I can't see it voiding your warranty as it is a mechanical variance and hard to trace if a problem occurs, and I presume the CPU will be able to control the fuel intake to boost pressure and protect the engine from potential knock.