The PayPal email you use to pay your subscription doesn't necessarily bear any relation to the PayPal email where you receive buyer payments. They can happen to be the same, but they don't have to be.
If you will be keeping the same PayPal email for your PayPal account when downgrading it from Pro to standard, you should not need to change your PayPal email with E-junkie in any regard; just make sure your Seller Admin > Edit Payment Preferences gets set to "Show PayPal Standard" instead of "PayPal Website Payments Pro".