I assume you cannot intentionally create illegal cargo situations just by using the free transfer rule?
Ex: A ship is full with 3 crew and 1 coin, she then loads a crew from the island and the coin is thrown overboard and removed from the game.
I’m seeing the restriction for exploring, but not for the crew transfer as a free action.
… choose as much treasure as you want to take (within the ship’s cargo capacity limits)
Edit: Now I’m seeing the Code ruling on cargo. I assume the free action of transferring crew wouldn’t be enough to voluntarily eliminate crew from the game either.
Cargo cannot be voluntarily eliminated or removed from the game unless an ability or action specifically allows it.
If an illegal situation requires the removal of cargo, you must remove crew and/or equipment before treasure.