Personally, when it is me in these situations, I proactively change my seat to suit the new aircraft operating.

With 9 months still to go, and considering CX only have 5 772 aircraft, it is very high chance the aircraft could swap again, so I would personally just check weekly/bi-weekly basis to ensure you still have a good seat on what ever aircraft is operating.

If you leave it too late, and the A330 stays, then you may find you don't have a good seat.