I mean, we could strat Rattler next season and tell Carr he's going to be the backup. That might actually make Carr ask for a trade and might make him willing to restructure his contract in order to make a trade possible.
But, I'd personally rather just let Carr and Rattler compete in camp and start whoever the better QB is unless it's really close at which point I would go with Rattler since he has more upside given his age.