A change in connection city is a re-route. For example, out of IAH, DL offers a lot of low fares when an ATL connection is involved, but not to the same ultimate destination via CVG. The markets this affects are those where AirTran competes. And when ticketed with a connection on a route where that same airline offers a non-stop, is considered a re-route and not allowed on a restricted ticket. However, it never hurts to ask at the airport, as some gate agents will allow you to standby when it involves a re-route. This is on a discretionary basis and will not be allowed by calling the airline in advance.