I am trying to book a one-way award consisting of two flight segments (operated by partner airlines), but the second flight doesn't have award availability yet. I booked a flexible (refundable) Aeroplan award ticket for the first flight segment. Adding the second flight shouldn't change the points required, though there could be a difference in taxes.

Should I:
1) Book the second flight as a separate award ticket immediately when it becomes available to reserve the seat, and call Aeroplan later to merge the tickets and get the excess points refunded, or,
2) Call Aeroplan right away to change my existing award ticket and add the second flight, and risk that availability disappears while I'm on hold?

Since flight awards can disappear quickly, my preference would be 1) so I can reserve the flight right away and call Aeroplan at a later point at my leisure to move the second segment to my first ticket and get my second one refunded.

Are they technically capable to merge and/or amend the tickets, even if the booked flights no longer show availability?