The op-up priority has been changed with effect from 1 August 2007, and looks something like this:

1. CX Diamond Plus
2. CX Diamond, CX Invitation
3. CX Gold
4. CX staff
5. CX staff nominees, Non-CX staff
6. Oneworld Emerald
7. Oneworld Sapphire
8. CX Silver
9. Oneworld Ruby
10. CX Green
11. Asia Miles
12. Non status

As Oneworld Emerald, you're a fair bit down the list so don't put your hopes too high. Are you on 110 from SYD? This is the only flight that still has F class.

Yes I'm quite sure that your FFP no. can be changed anytime.