I redeemed a round trip PY HKG/NRT ticket and have already used the outbound sector. Few days ago, CX informed me that the due to equipment change, they have rebooked my return flight in Y and will refund the mileage differences. I reluctantly accepted as my work schedue was fixed. Now there is a last minute change of my work schedule that I can travel on a different date so I called CX to change my reservation. Still, there is no PY available for my desire flight so I decided to go ahead with booking Y. Surprisingly, I was told that in such case, my ticket would need to re-issue and there will be deduction of another 10000 points or USD100

Am I being double penalty? Involuntary downgrade + extra cost of reissue ticket