I booked the ORD-SEA-PVG, PVG-SEA-ORD roundtrip cash ticket (V->SU) and have flown the ORD-PVG. I am currently sitting on the PVG-ORD return on 11/30, but I need to change it to a later, currently unknown date in december.

I checked the change fee to the same flight on some random dates in december and all of them are showing a $0 difference in fare, which is odd since the tickets have gone up in prices since I booked.

This is good news to me, but if I change it now to some placeholder date in December, will I lose the current no-change-fee ticket when I rebook again?

TIA