It is quite interesting that CX allows to use historical fares before the outbound flight when you change a ticket from TPE/KHH. That means that you do not have to pay the fare difference even if fares increased a lot. Of course, that is often accomplished by playing with fare bucket availability, but still surprising.

Regarding standby without repricing, I doubt that an a CX check-in agent at KHH would allow it without a good reason.