You are able to create coupons for all your products. Once you have created a product, go to Pricing and Actions. You will then see a list of actions, go to Coupons and + Coupon code.
Add in the coupon code and discount percentage and select Create coupon.
Please note coupons can be used for the duration of the membership. So for example on a monthly basis if they are billed monthly until they terminate their membership with you.