Hello all, hopefully this will be an easy one for some on here, would be grateful for any information.

If I book a LHR->SYD flight with my Avios (possibly using an Amex 2-4-1) is it possible to change the return date at a later point?

Obviously subject to reward availability on my new return dates but what kind of fees can I expect if I was to book any old date initially and then request a date change later on?

Circumstances dictate I don't have a firm return date as yet. The change would probably be requested after the outbound flight had taken place if that makes any difference at all.

Thanks in advance.