I'm booked on VN255 HAN-SGN, 16:00 departure on 26JAN in Y. Looking at the seat map the flight is scheduled to be operated by an A350-900 with a 2-4-2 configured Premium Economy cabin. I do not have SkyTeam status but I can pre‐select seats in this cabin even though it's Y class service.

I am not a frequent VN flyer, how often are aircraft switched/downguaged on this route? The first two rows in this cabin are blocked for seat selection. The fee to select a seat is very reasonable, approx 11USD. The seat map currently shows all seats available for pre‐selection except rows 10 and 11. Looking at the flight history it is mostly operated by an A321 with the odd B787. I don't want to pre‐select a seat now and then have a change of equipment later.