Hi,
It's possible yes. Create a discount (menu Orders>Discounts) and restrict it to a specific user group that you will have created in the Joomla user manager. Discounts, unlike coupons, are applied automatically to the products if the restrictions match the situation.
Then, configure a mass action (menu System>Mass actions) so that you add that user group to the users when their order is confirmed. That way, you'll have them to a new user group after their purchase and they'll have the discount applied to the products automatically.