Just trawling through the T&Cs on changes which are (generally) as follows:
Changes after ticketing and up to 24 hours prior to commencement of any travel on your Itinerary
14.5.10 Subject to this clause 14.5, the following changes are permitted and a Change Fee per passenger will apply (see the
Fee Schedule):
(a) change to flight number;
(b) change to date of travel;
(c) change to class of travel;
(d) change to any Segment routing or airline [segment being the portion of a journey between two consecutive points listed on an Itinerary]; and
(e) change to name (only for Flights with a Qantas (QF) flight number on the ticket that are operated by Qantas).
Changes to a wholly domestic Australian Itinerary after commencement of travel and up to 24 hours prior to commencement of any subsequent Flight Segment
14.5.11 Subject to this clause 14.5, the following changes are permitted and a Change Fee per passenger will apply (see the
Fee Schedule):
(a) change to flight number;
(b) change to date of travel;
(c) change to class of travel; and
(d) change to a direct or indirect Segment routing without a Stopover (provided that the origin city, the destination city, and the airline remain unchanged).