Two Loyalty Numbers
 

I don't think this is possible but would love to be corrected if wrong. I have SAS Gold Status, but would love to claim the points with my Virgin account (Silver). Is this possible at all or by doing that will I lose my SAS privileges for the flight?

The best way to do this is: Use the EBG number during check-in, enjoy extra bag, priority check-in, fast track and lounge. Then when you are in the lounge, change to the Virgin FFP number. Or do it at the gate.

But chances are 50/50. Sometimes the FFP number used when the boarding pass is issues is "stuck" to the booking.

Thank you - to make matters more complicated, I'm doing a connecting fly!

I would highly recommend to get a bp with the changed FFP account. Often had they said yes, and then it wasnt changed....

Well, then you need to switch back to the EBG at your connecting airport. This might work, might not work. Last time I tired this was some time ago and it did not work for me (CPH-DEN-SJC), and UA did not let me attach my EBG number to the DEN-SJC leg making up some absurd rules that it is not possible.

even that doesn't guarantee the desired crediting... I have numerous boarding passes which says e.g. LH*G and still credit went to SK or vice versa.

It won't work for baggage benefit (you will have an unpaid bag detected at boarding), but will for everything else.

Change the FFN yourself, don't rely on agents.

Honestly, never had that problem…

if possible yes, but often enough it seems the FFP is stuck after check-in. Only way I found, was the gate agent. But YMMV…