Changing multi-city ticket
 

I am running into an issue with a multi-city ticket. It goes City A - B - C - B - A. I am booked in D class from A to B and B to C. I am attempting to change B to C to another city that meets the fare rules of the ticket, but there is no longer D availability on the A to B portion. There is D class available on the new flight from B to new city and the agent confirmed it does meet the fare rules, but because there are not two ADDITIONAL seats available on A to B they can’t make the change.

Does this seem right? I have two D seats on that flight, why do they need two additional seats on the leg I’m not changing to make the change?

I'm assuming you are pre departure on the outbound leg. Since the whole ticket needs to be repriced anyway, why not just book a new PNR and apply the credit from your current one to the new one?

They are telling me that if I cancel my existing ticket there is no guarantee they’ll be able to rebook it immediately in D class, that it might not go back into inventory.

Why are you worried about D class specifically as opposed to whatever today's lowest first class fare is?

Do you have the fare basis codes for each of these legs? That will help to look up the specific fare rules for what happens when the ticket is changed pre departure.

Should you be looking for married segment fare class availability A - B - NewCity? Or is there a stopover at B since you're saying multi-city rather than just a RT with a connection at B in each direction??

Only because that’s the cheapest business fare bucket left on that itinerary, for this routing it jumps straight to J and doubles the price.

There is a stopover in B.