Yes you can! Pay only the difference when upgrading. For now, purchase the premium license. When you’re ready to upgrade log in to the Avalanche member portal. Select the “Add/Renew Subscription” tab. Finally, select “Avalanche Premium to Developer Upgrade” from the membership type dropdown.
The developer license allows unlimited use of Avalanche on sites that you own. In other words, any store where you are listed as the owner of the domain.