I'm not wholly sure how Jacksonville operates because I didn't work there, but when it comes to redemption flights on BA, I regularly removed single sectors prior to 24 hours before take-off. This returned all money and all avios less GBP40 reroute fee. I never did it using AA prime flights (must be used in the case of avios redemption on partner airlines) but I can only assume that customers are subjected to precisely the same rules. Redemption tickets and comms tickets have dichotomous rules.