So it says that you can only purchase Duty at character creation. If you have players that want to purchace into talent trees in AoR, would you allow them to purchase into Duty if the character is already made. Atleast until either the actual book comes out next year, or hear back from the developers.
I would suggest not. The idea is that new characters have a back story that might suggest previous duty tours with the rebellion. Most existing characters would not have that back story. If they did, then I would consider it when they "rejoined" the rebellion. But that would be when they actually rejoined in story, not just selected a specialization.