Richard at TIFF Talk noticed a change in the ticketing policy:
Thanks to Greg from TOfilmfest.ca for pointing out that in the latest mailing to festival goers, it lists that if you want to exchange a ticket to one film for a different film or screening, there is a $2.50 charge per ticket. Tickets can be exchanged up until the day before the actual screening.
He also offers some advice for minimizing your number of exchanges. I decided to buy the full 50-ticket Festival Pass this year, which will give me 10-15 extra vouchers to play with. As Richard notes, rather than exchanging a real ticket, you can always sell it to someone in the rush line. I usually walk to the front of the line, hold the ticket in the air, and sell it at face value. There's always a taker.