Advice on changing reward booking

Wonder if anyone out there can help?Mr DL and I have both booked reward flights (G) to LHR-SFO return in October. If I change the flights to one G to SYD (which I believe I can do without major penalty can't I- or would there have to be 2 bookings not to lose miles??)will I "pay" the old rate to SYD that I would have paid when making the SFO booking or the new heftier rate??[?](which will be a good few Ks more than it was).Hope that makes sense- I'm getting really confused.
Thanks
Julie

[preiffer]

Since it's a route change that requires a recalculation of mileage, I *believe* it'll be at the new rates.

ISTBC, though [:I]

Bah humbug -if memory serves me right the old G fare to SYD was 160,000 miles but is now 180,000 miles.
Thanks anyway.
Julie

[RichardMannion]

Originally posted by DragonLady
Bah humbug -if memory serves me right the old G fare to SYD was 160,000 miles but is now 180,000 miles.
Thanks anyway.
Julie

Nope - SYD rtn in Upper has always been 180k. Its 100k for the LHR-HKG sector, then 80k for the HKG-SYD sector.

Thanks,
Richard

Ah my mistake Richard- I thought the two legs were both 80k.Don't feel too bad now (as it won't cost any more miles than it would have).
Thanks
Julie