Actually, although most VW dealership mechanics will do as you did, setting the length of the rod to be the same as the old one, in practice that's not always the proper thing to do, as the old actuator probably doesn't have the range of motion that a new one does, and the rod doesn't spring back to the fully extended position.
You should get under the car with a vacuum pump (Mity-Vac or the Princess Auto / Harbor Freight equivalent... you should adjust the actuator rod so that it begins moving at 3-5 inches Hg... A final check that the actuator is fully open at 18 inches is also needed...
It's not so much the absolute pressure that will be affected but the rate of turbo boost applied... if too much (or too little) boost is applied at any time, the car's computer will complain, as it expects to "see" certain parameters at certain times.
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