Welcome! Yup, that's doable, although we need to sort it out manually
Easiest way is to send an email saying you'd like to upgrade to the Special Edition to firstname.lastname@example.org
, bonus points for using the email address that you previously bought the game with (the one tied to the PayPal transaction). We'll send you a $10 bill and once that comes through, upgrade you to the SE via our backend.
Be warned that the Special Edition content isn't in the beta yet, so you won't get access to anything extra right now.