Streng genommen muss deine Frage mit "beim Boarding" beantwortet werden.
Die Geschäftsbedinungen lauten bezüglich der Seat Reservation wie üblich:
We will endeavour to honour advance seating requests. However, we do not guarantee to provide any particular seat in the aircraft. We reserve the right to assign or reassign seats at any time even after boarding of the aircraft for operational, safety or security reasons and you agree to accept any seat that may be allotted on the flight in the class of service for which the Ticket has been issued.
(Quelle: QR CoC)