To reduce the wastegate opening pressure you need to pull it apart and change the spring inside of it. However changing it to open at 1 psi would be the dumbest thing ive heard today. Your wastegate would be just about always open, and for instance trying to drive up a hill with no boost cause your gate is venting all your exhaust gases would drive you nuts.
Your drivablitiy of the car would go out the window as it would be a slug, you know like driving grandma's Hyundi.