I have been told that a B-RNAV equipped aircraft can fly a P-RNAV arrival as long as it remains above the MSA.
I have never heard of this.
Anyway, arrivals (I assume you mean SIDs/STARs)
are flown above the MSA. Only the IAP that follows the STAR takes one below the MSA.
And there is no such thing as a PRNAV IAP.
PRNAV is a tricky thing at the moment. The guidance document (TGL-10 I think) is a load of vague bollox and is being interpreted, shall we say, creatively, by different avionics shops and by different people not entirely unconnected to the UK CAA and Eurocontrol. I am not aware of any G-reg GA light aircraft that has got PRNAV approval (for real I mean). N-reg, yes; there is a route via a LoA. But this is not my speciality - never had to do it and fortunately only a few SIDs and STARs in Europe are PRNAV and all such airports have non-PRNAV ones too - they have to since most large aircraft are not PRNAV compliant. I don't believe there is any PRNAV
enroute airspace that is significant to GA, either. If there was, we would have a major problem.