Shortening and lenghtening the actuator rod is NOT the way adjust boost. The rod preload should be a few millimeters and never much more than that. Boosst is then adjusted by controlling how big a portion of the boost pressure reaches the wastegate actuator. Of course selecting a suitable actuator in the first place is crucial.
The in car boost adjusters are most ususally just valves that make a controlled leak to the wastegate actuator hose. This is usually referred to as bleeding and the valve a bleeder.