Originally Posted by
Often1
This is largely a failure to invest in IT. Front line agents have less training than in the past and should not need it. Rules-based features such as SDC are what software exists for. All an agent should need to do is to pull up what the customer wants to do and the software ought to determine whether that is doable and what it costs, if anything.
The rules say that one can't change origin or destination airport. The OP was seeking to SDC (not standby) after he had already departed the origin.