If you wan't to become a co host yes you will have to do that, create a new listing. Problem is you'll lose all those reviews and whatever reputation was attached to it. You may be able to change banking info, once they removed cohost payouts this was the way they recommended to continue paying cohosts. Basically a primary bank account for the host and secondary bank account for the co host. Each gets a percentage. He'd have to be the cohost.
I'd call AirBNB directly to confirm this is okay and not violating any terms of service.