I do not recommend it. Even though prepaid and postpaid are 2 separate systems, there have been reported issues in the past. I would highly suggest you use a different email
As far as I'm aware, no, you can’t. Only one self-serve account can be used with one email address at a given time. When attempting to sign-up for the prepaid, it should tell you that the email is already assigned to another account and not allow you to proceed.
I suggest you use a different email address for the new account.