Yes, do this. Then you're likely looking at a change fee (on the order of $250 - $275 since this is international), plus the difference in fare. The latter can be a plus or minus (really, I had a fare go down by about $23 2 days before departure than helped offset the change fee

).
Oh, and
vrbaba was remiss in not welcoming you to FT
Cheers.
Ah thanks, that's really helpful. Who can make this change to the reservation? Does it need to be the original person who booked it, or can it be one of the passengers? Will the change fee be applied to the original payment method, or can I provide another card number?
...also, given that YYZ is at least geographically on the way to VCE; the fare difference shouldn't be too significant, should it? i.e. <$200?
Thanks for your replies, FT's a fantastic place.