I checked the N75 today on my LCR, i could not see the screw you were on about, i pulled a 1.8bar spike tonight which is too high IMO.
there is a little 6mm hole on the top of the n75 the screw is in there mate the thread will be locked in place but it will turn once cracked i would just turn it a quarter turn clockwise to start with then log it i was amazed how smoth it made the boost i would have no more than 1.5 bar really mate so have a go and see just check boost, n75 duty cycle ,fueling etc with vag com when doing it, i just used a spare n75 i had kicking about to have a play i was shocked the diffrence ither way it made