Deleting Primary E-Mail Acct

You really can't delete it.  You can change it, but keep in mind that the primary is your sign-in credential for your entire Comcast account, not just the email.  Just stop using it.  If you want to keep it from getting any new emails, go into the settings and enable the safe list.  Put some other email address you have on that list and nothing else.  It will then only be able to receive emails from that address.