When you archive a coupon code, it will no longer work for new clients. However, payments will remain unchanged for any client who has already used the code. For example, if a client used the code to get 20% off their ongoing subscription, their payments would still charge at the discount price after you archive the coupon. Note that it won't work to add an archived coupon code back to the package. If you want to add a coupon code back to its original package, it'll need to be a different code. (Or, you can make a new package and re-use the original coupon code.)