My friend has just lot his national ID, but still has his passport with him. Can he identify himself with the passport instead of the document used when he checked in online with Ryanair?
Based on plenty of intra-EU Ryanair flights I never had the impression that they check for the indicated document but just a valid document matching the passenger. It's not indicated on the boarding pass and don't think they can see it on the computer. Probably I have already travelled with a document different from the one indicated online and nobody has even noticed. I would not worry too much about it.
That may well be different from what official sources tell you.