You can commission so many BOs based on your rank. If all your BO slots are full you going to have to hold on to him in the que till you rank so you can add them to your team. Otherwise your going to have to release one.
Retraining a new BO is not that bad... I was surprised how quickly I trained new BOs to reach the same skill points I had before on an old one.
It would still be nice if you could Decommission instead of Dismissing an Officer outright if your slots are full. Something like sending your Officer on assignment or leave. I dislike losing them if my slots are full and I gain that "perfect fit" as a quest reward. Maybe a Decommission option with a reasonable cooldown would be in order.
Seriously, everyone plays these kinds of games differently and has different goals for the game. I hope that role play increases. My first BO that I received was a common Andorian female with looks that go nicely with my toon. Shes not very good and I have BO's that are obviously better. But you would think that I would have a spot on my ship for her even if she wasnt the best Tactical Officer available on the ship. Then I found, Shran the Andorian on the exchange who I have not used and slotted. His stats are pretty bad but it would be a world of fun to have Shran around on a RP basis. Eventually, I would like to have a team of Andorians for RP and then perhaps a team of "others" who would be actually good characters that were good at their jobs.
I guess I will have to fire my Andorian BO but as a Captain who feels loyalty to his crew this kind of irritates me a bit. I guess that I could train her up and make her "close" to as good but I lucked out and got an efficient Saurian and I dont think efficiency is a trainable skill so shed never be "perfectly" as good as the Saurian even though she blends better with the ship, its captain, and its crew on a role play basis than the Saurian with efficiency.