Staff at TPE tends to be quite strict for such changes. They have so many flights to HKG, that it gets very messy if they keep changing non-changeable tickets.

Your hope is if that CX531 is quite full and they might need your seat. Actually, the load for Monday 18 looks quite high so you might have a chance.
Note that your connection in HKG is quite short, and the evening flights tend to have a 30min delay. It might be wise to try to get on an earlier flight. The counter will have some indication of delay if the plane is late departing from HKG, so they might be receptive. There are four CX flight between 5:45 and 7:35pm