Originally Posted by
anabolism
Changing the carrier requires a reissue, I believe. Likewise, if one tickets a flight in L on a DONEx, and later D opens up or one switches to a flight that has D, the $125 fee has never been charged even though a change to booking code requires a reissue.
General IATA rule is that a carrier can revalidate the ticket with a change to carrier, but a TA would have to reissue to change the carrier. Change to booking code can be done with a revalidation in both cases. But only if the taxes are unchanged of course.