Naturally without an adjustable wastegate, the boost is pretty much dictated by the burn of the chip. And yes all you have to do is put on an adjustable wastegate and you can raise or lower boost that way
Chip controls when the solenoid closes (which opens the wastegate). Wide open solenoid = infinite boost. Cycling the solenoid open and closed increases the boost over the "solenoid closed" setting.
Shortening the wastegate rod raises the "base boost". If the stock boost is 14 psi when the solenoid is closed, a .25" shorter rod will be about 19 psi with the solenoid closed.