The choreboy is mostly a 'joke' position, which as such makes less sense. "Did you hear that the 'future of the marines' was once the pirate king's chore boy?" sort of irony.

As for Luffy, he hasn't officially made anyone any role that they weren't already before. Like he was full on ready to take in Brook without knowing he was musician, or Jimbei before he showed his helmsman ship. Roles are something they chose for themselves. Would Coby submit himself to the lowest position on the crew? He has humility and sensibility to know he doesn't quite fit, so I would say there's a high chance.

(I think Carrot and Yamato wasnt sure who they were currently and they would fit in the crew, as neither did the readers when we were coming up with random roles for Carrot or Yamato to take. Ussop may seem like the weakest link in this argument but he knew himself as a liar and coward who )