I have spare accounts, but log out and log in just for the sake of beta is an absolute pain. So I just use my main account for the entire beta process. If I have sth That can support me restoring 400GB of data in 8 hours then I might consider.
As for downgrade, while you technically can downgrade from beta, the data accumulated during beta process might be irretrievable. The longer beta goes the more you lose. Very Apple-style one way street.