Originally Posted by
jmanirish
Surprised nobody has commented on this part. Right now there is no public waiver for HKG flights, so you should've been charged a change fee. If there was a waiver, then those rules would apply. Some require the same fare class/code to be available, some only require that it be the same cabin.
They either waive the change fee only, or both the change fee and difference in fare. Nothing special about same booking code.