Henrik,
We reviewed the XR200 recently in HAM, maybe you've seen it here
Diana XR200 PCP Air Rifle Review .22 Caliber - Hard Air Magazine
You are right, the screw adjustment on the left side of the breech can be used to alter the power output of the gun. But it is - in fact - a "transfer port adjuster" and not a regulator. The regulator in the XR200 is set at one fixed pressure in the factory.
In simple terms, this means that adjusting the screw on the left side of the breech allows more or less air to be effectively applied behind each shot. You can experiment with different settings without fear that you are changing anything permanently. No problem!
I hope this explanation makes sense...