I had a search, but couldn't find anything directly relevant with RFS and partner in the title, beyond some chat about Iberia and making changes to an RFS onto a partner airline

My understanding is that RFS is only possible on BA flights, so that a partner flight (in my specific case, would be AY) is regular taxes/fees.

However, could I get a single PNR for LHR-HEL (RFS on BA) then HEL-oop north (regular avios + taxes on AY)? I know that I could book separately online, but this would be for peace of mind w irrops, given that it will be for Xmas ().

And I know that I'd need to do it over the phone and pay the service fee, but it's for the family and therefore amortises quite easily...