Originally Posted by Oaxaca

Ok, short update on this. I've now created an IB+ account and a Vueling account with my IB+ number as the primary FFP with VY. Will see if that works for seat selection going forward.

However, my current booking already had a BA number in it, which complicated matters slightly, but meant I found another way to do seat selection on VY with a booking on IB.

In order to change the FFP number in the booking from BA to IB+ (Seemingly not possible on IB.com, similar issue on BA.com), I tried Manage My Booking on Finnair and Royal Jordanian websites. Finnair wouldn't work (wouldn't recognise the IB+ number), but RJ.com did work.

I entered the 6 character IB locator and my name into MMB on RJ.com, and got into the booking. The resulting booking record showed another 5 character IB locator. After changing my FFP in the booking to IB+, I tried putting this locator into VY.com, and it worked! The booking appeared with the VY locator and I was able to change my seat from the pre-assigned one.

May not need to do this in future if having the IB+ number in my VY account works, but seems there is at least one other way to get into the booking on VY.com.

[edit : when I got to check-in at the airport, the FFP number was still showing BA in the booking, so the RJ.com trick didn't work for that. It worked fine for finding the VY locator to do seat assignment though].