With the Injury system, it's possible for a Bridge Officer to become so injured that it may be more effective to replace him, instead of using up Regenerators. (Which you may need for yourself! ) I had actually hoped the "Request Reinforcements" button would allow me to do something like that, but it appears to be available for replacing player teammates and not BOs. (It doesn't even show up most of the time, it seems to only appear when you have an Away Team of two, and then doesn't work)
It is possible to just beam back to the ship, select the mission again, and then change your Away Team layout. However, when I do that I'm always a little afraid I will reset the mission. Plus, it can just be dangerous to leave a position where you are relatively safe, beam back to the ship, and then beam down again to a random location where you may have to approach your target all over again. If I could just select a Bridge Officer, select, "Beam back to ship", and then click the Reinforcements button (assuming I get to choose the replacement) then that would be a lot simpler.
I can see the possibility that being able to switch out Away Team members at will could be imbalanced, but in such a case, it might be possible to just make the option greyed out until the Away Team member has at least taken a Minor Injury. Alternately, it could have a cooldown, so once you switch out an officer, you can't switch another for several minutes.