All components in your plumbing system, including the toilet and its supply lines, are designed for a test pressure of 150 PSI. The normal operating pressure should not exceed 80 PSI, and your house should be built so that is does not ( PRV installed if necessary). There is no code requirment to PROTECT your house should the pressure go higher. The expansion tank will help to keep the pressure much lower than that 150 PSI number.
A bypass on a PRV will only keep the house pressure from exceeding the street pressure. That is of little comfort is the street is well above 100, maybe above 150.
I don't understand about the silent blowing and the gunk???????