In reply to the original question, Make sure you know when the RNP should change before making manual changes.
On the E-jets when flying NPA using FMS as primary nav source the RNP will change to 0.3 only 2 miles before the FAF. This is by design as before that the approach is RNP 1. If you change early and get a degrade you should go around by the book but if this is because you manually changed the RNP early it's your own mistake that caused the go around.