I am trying to change a departure from LAX to BUR. From what I have always understood, as the two airports are co-terminals, it should be posible to (for a change fee), change that airport without a ticket re-issue.

Half the time, agents do this without problem. But much of the time, I hit a wall.

Today, one agent said, "Only full fare ticket allow for changing within co-terminals."

Another, "You must change the ticket at least 7 days in advance."

Another, "Only on certain, time-verified fares."

Is there a definative rule?