You select a Branch in the Job Menu, and your character is sealed to those jobs within the branch.
Branch Civ: Cargo Roles, 'Crew' Roles (Chef, Assistant, Bartender, etc.) (Head Included)
Branch Sec: Sec Roles (Head Included)
Branch Med: Med Roles (Head Included)
Branch Engi: Engi Roles (Head Included)
Branch Sci: Scientist Roles (Head Included)
Branch Command (Unique): All Players with Whitelist + Required Branch (Captain/IAA Command Whitelist Restricted Only)
This Means a Branch Civ Character that gets a Head Whitelist can go HoP, Captain, and IAA.
A Character in the Med Branch with a Head Whitelist can go CMO, Captain, and IAA.
6 Day Cooldown before it goes into effect to find the Job that the character is best suited for.
This also could be paired with the Eco Update.