I think that Chewie most likely crewed the turrets in combat, switching between them as needed. Han wouldn't have installed those (or mounted automated ones) if he needed Chewie in cockpit during combat.
I really like that retcon, anyway. It really makes a lot of sense. If the Falcon was a space tug first and foremost, it was really just the thing to modify the way Han did it. It must have already had powerful engines (if not fast ones), a powerful steering system and a reactor to power all this. Also, while authorities routinely scan cargo containers, scanning the tug is most likely something that's often forgone to save time (or simply out of lazyness). TBH, I wonder why did it take so long for someone to think of this.