I have a half-used round trip, i.e., itinerary from AAA to BBB to CCC, and having completed AAA to BBB, I am in BBB. How I ended up with this is a long story.

Anyway, after using BBB to CCC, I need to get from CCC to BBB. The one way fares book into Y at a price that is breathtakingly prohibitive, but there are S fares available, just not as one-ways. My existing fare is V or something.

One solution is to "lose" my BBB-CCC ticket and just book BBB-CCC-BBB round trip in a lower fare bucket.

Before I come up with that kind of strategy, can anyone tell me whether it is possible to add an S-class segment onto an existing PNR like this?

Thanks!