I have booked and am about to pay for flights from MEL to PVG return, I used the seat guarantee to get the V class prices and was told that flight date changes would be free of charge.

However as only higher classes are available does that mean that if I wanted to change my flights I would have to pay the difference? or does the seat guarantee still count and I remain as V class but on a different day?

I understand that I could leave it to 72 hours before the flight to have a better idea about the dates, however this would not be very convenient as I want to pay now.

Thanks in advance!