Recently, I had to change a Star Alliance award due to a family emergency(from YOW to Malaga, Spain, with a stopover in Zurich). I was in Spain at that time, when the change had to be made.

I did not realize it, but I was told that once you used part of the Star Alliance award - you can only change the dates of the return; not the routing. I was booked to return from ZRH to YOW via LHR and YUL - I wanted to change it to an earlier date from ZRH to YUL (via LX) and then on to YOW. Fortunately, all worked out.

I was also told that such type of routing changes are allowed for a Aeroplan award involving AC flights only.

In terms of what I could find for terms and conditions for change of Aeroplan rewards, and for the basic rules of Star Alliance awards (on the Aeroplan web site):

https://www.aeroplan.com/help/topic.do?id=3002

http://www.aeroplan.com/terms_and_co...rdstaralliance