If I might add a bit of confusion here:
Players Guide p155
<B>Sechok chooses to become an envoy ... he decides to forego advancement as an explorer ... next time Sechok advances, he could chose to re-enter the explorer elite profession by spending another 5 picks. After returning to the profession, he could resume development of explorer skills and abilities ...</B>
So changing back to a former profession is still not free ... does this mean that when you chose in which professions you want to advance, you have to keep your base profession? This doesn't seem right, as in the above example, Sechok has chosen Envoy and Science Officer. Obviously he had already given up the Starship Officer base profession.
So ... how much would the switching back to the base profession cost?
Every procedure for getting a cat to take a pill works fine -- once.
Like the Borg, they learn...
-- (Terry Pratchett, alt.fan.pratchett)