Thanks brunos. It is obviously easier if I can keep both flights on the one ticket, both because of possible flight delays and missing the second flight and as you mentioned, of probably not having bags checked through.

I've been looking at the Asia Miles FAQ page and see the following under "Change Booking" so this may apply in the situation I am querying:
https://www.asiamiles.com/en/support...ight/general/1

2. Can I change the destination after my ticket has been issued?Yes, a completely unused ticket can be reissued for a service fee of USD100 or 10,000 Asia Miles subject to:

• The new ticket having the same expiry date as the original ticket.
• No changes regarding the operating airline.
• No changes regarding the passenger name.

In this case I would be changing the destination from LHR to ZRH with other details being the same as above, by adding the LHR-ZRH flight so hopefully this would apply in this circumstance.

When I have booked award flights through QFF in the past I have been able to book initial flights online as soon as they were available and then call up to add more flights to the same PNR and pay a 5000 points change fee when later flights became available. You can only do this by adding to an original booking and not by booking 2 separate flights and asking to combine them later. This was when booking One World Awards through QFF where I had to use two different One World carriers besides QF and gradually added flights over the phone when available.

I used Asia Miles to book a redemption flight once back in 2018 when I transferred Amex points to Asia Miles and the points required for ZRH-SYD via LHR in 2019 on BA were a lot lower than when booking the same flights through QFF. I have flown CX multiple times when J flights were available but haven't seen much award availability when I was booking in 2019 or when doing dummy searches at the moment for late 2022. We will be doing an Antarctica cruise from Ushuaia in January 2023 and will need to get from SYD to EZE, then EZE-ZRH, then ZRH-SYD in J. At the moment the best way I can see to get from SYD to EZE will be to book SYD-LHR then LHR-EZE, even though it is a long way around to get there at least it will be in J. I never seem to see award availability on QF to fly SYD-SCL as a Bronze QFF.

I am still learning about using Asia Miles and the various differences to using QFF that I have mainly been using up until now so appreciate advice from others who have more experience than me.