You better call the Canto hotline to make sure they have remarked that they will refund the difference, English and Mandarin hotline CSs are less experienced and can only handle simple issues.

Calling the Canto hotline amy be able to have your return leg ticketing deadline postpone to T-7 of your inbound which should have more than enough time for you to see if your outbound will get cleared.

I think the J seat map is relatively accurate because CX will assign a seat for all (or most) J passenger. In contrast, Y is less accurate because many passengers have no per-assignment.

I dont think it is that necessary to move your R booking around. You better just call periodically to check if any upgrade redemption seat opens up within that period.