So you fly an attack sortie that turns out to not be needed for the base capture. So you want to swap that sortie for a fighter sortie, even though it's really a new sortie. Sounds like you are very concerned about your score and the "kills per sortie" rating. And you probably will fly that fighter sweep in attack mode; to preserve your fighter score.
Makes no difference to me whether this wish is implemented or not - game the game as much as you want if that's what's important to you. I highly doubt HTC would be spending the man-hours and payroll to add this feature just so some people can play this game "more gamier".