I can comment on this matter as I have done this twice with Aeroplan. In my case I wanted to fly Sydney to Toronto with a 2 week stopover in Zurich followed by LA to Sydney with a couple day stopover in Seoul. I managed to initially find and book SYD > ZRH and LAX > ICN in business. Later, when ZRH > YYZ and ICN > SYD became available I called up Aeroplan to get them to add those legs on.
There are two things to keep in mind here:
- You may have to pay a change fee to add the segment later on. If you booked the flight as a Business Flexible award there shouldn't be any fees, but the normal business award will attract a fee of around $100 CAD IIRC
- When you make that change, Air Canada will have to reprice the cost of the ticket as the award chart (at least for partners like Turkish and Singapore) use a distance based chart to determine how many points are required.
With all of that being said, if you do find availability on a partner like Turkish in business, don't hesitate and pull the trigger. Availability can change rapidly and I cannot tell you the number of times I missed out on an opportunity because I waited a few hours or a day.
One last point, if you are looking to do the stopover option (i.e. fly MEL - SIN, stopover in SIN then fly onwards) you can do all of this online for free. Here is an article on how to make that booking:
Aeroplan's stopover rules permit travellers to squeeze in an extended stay on a one-way trip to most places in the world for only 5,000 extra points.
princeoftravel.com