As far as I'm aware you can't "shim" the pressure transmitter (it's a hydraulic transducer that responds to pressure) - the thing you shim is the oil pressure release valve spring. Adding more shims puts more pressure on the release valve piston and thus increases the pressure at which it opens. I can see the logic of putting a lot of shims in for the first run to ensure a healthy oil pressure for those important first few minutes of running, but as it's the actual oil pressure which is excessive (not just the gauge reading) it should be reduced to the specified range as soon as practicable because running in that condition will have all the consequences previously described.
But I am confused - if this was a "new" engine then the oil pressure should have been set at the factory because engines have to be bench run in a dyno (actually several bench runs at a range of power settings and durations) before being released for sale. If it was an overhauled engine it should also have had a number of bench runs before release - these are certification requirements. If a new or overhauled engine was installed without a correctly set oil pressure relief valve then the company who made/overhauled it seem to have been playing fast and loose with release certificates...
PDR