I think it depends on fare class policy of the departure city and route, in this case, Japan to Hong Kong, China, Southeast Asia, Northeast Asia.

I class for this one is listed here:

https://www.cathaypacific.com/cx/en_...ode=JP&class=C


There are also restrictions on how many days before departure you are allowed to change. And some require 4 weeks or more lead time, otherwise they won't change it for you, even if you pay the rebooking fee.