You can assign affiliates to existing customers as a “lifetime affiliate” by going to the “Users” list in the admin area, then edit the user profile for the customer, and go to the “Coupon Affiliates – Lifetime Affiliate Settings” section.
Here you can enter the coupon code for the affiliate, which will then assign that affiliate to the customer for all future orders.
Any future orders made by that customer will be assigned to the affiliate, so they will earn commission, and the order will be displayed on the affiliate dashboard for that coupon. However, no coupon discount will be applied to their order.