Originally Posted by jsloan

For voluntary changes? Generally, no. The exception would be if you’ve already baked in a stopover at B — in which case you could change the date of the B-C flight — or if B was a fare break, in which case you could change the date or destination.

Trying to do anything else is going to result in an exasperated agent and a fare difference, if they can even calculate one, that likely runs into the thousands of dollars.