I know where to get new ones and how much merit they cost, but what If I don't like one of them and I can't change them, is there anywhere I can go that I can trade BOffs or just sell them for some merit? All I see is the option to dismiss them.
Once they have joined your crew... you cannot sell nor trade them. Dismiss is your only option.
But... if its their skills your not happy with you can go to the power store right next to the req officer and buy better skills, and if its their appearance just use the tailor when you get some credits.
That being said if its the race or gender your not happy with... then the airlock really is the only option.