Downloadable product...built to order?

We have a downloadable product that needs to be configured to the individual customer. I was wondering if there’s an individual download available only after the order has been processed…i.e…

  1. customer purchases downloadable product and checks out
  2. customer service configures product, adds to (???) where it can be accessed by the individual customer
  3. customer service updates order status to complete and customer is notified
  4. customer logs into account where download is available

    I have not found a way to provide a one-off/customized download to a customer. Am I missing something? v2.1.2