I just harvested $108 in credits by rebooking this way. awesome. I'd have done more but the 3am deadline from the fare sale ending hit right as I was confirming another 2 flight changes.

If the flights had a stop between a-b and between b-c I got $9 back, if only one of the directions had a stop I got $4.50 back. If neither had a stop I had to skip rebooking that route and move on to the next flight, since the savings would be $0