Coupons on an eticket must be used in sequence. Any coupons that are before a used coupon become forfeited/used.

So in a case like this, the only way to preserve your outbound is to first change it to a later date, then cancel, and then eat the change fee a second time. Aeroplan style.

So to save it, you will have to pay the change fee twice + fare difference. Plus if your departure city becomes YUL instead of YVR, you will have to be reassessed at 15% sales tax (GST QST) instead of just 5% for YVR. Probably why the agents told you it's not worth it.

The sales tax advantage is a reason why you don't want to book one ways out of certain provinces, but not out of others.

In case of IRROPS, AC will cover a series of separate 014 AC only tickets all the way back to your point of origin. So it's very "safe" to do in NA.