Try here to look for fare conditions:
https://www.cathaypacific.com/cx/en_...nditions.html?

Select originating from US.

It appears all the Economy fares have rebooking fees. V class would have a rebooking fee of US$100 (as it is definitely not Economy Flex).

It really depends on your luck on the day. Even as a DM on a business class ticket which had a rebooking fee, I've been asked to pay to get on an earlier flight. I've also been asked to pay the rebooking fee in economy class as a GO.

But on other occasions I've been able to get on an earlier flight with no fee needed (again in economy class as a GO).

All of my experiences were out of HKG, trying to get on an earlier flight to TPE instead of hanging around in the airport for an hour.