Second this! There are many reasons a payment plan may need to be restructured over the course of a project. I currently have a client who had an opportunity come up unexpectedly that made her website higher priority than other items in her package, so we moved it ahead of other milestones on the schedule. I had to create a new payment plan for her. In another case, some elements of a project will be delayed. I'd like to invoice now for what has been completed, but I can't add a milestone at the correct point in the sequence, or generate the next invoice without indicating that the project is completed. It's odd that we can add milestones to an active payment plan, but only before the deposit...? It would be great if payment plans could be fully editable, both in terms of the sequence of payments and the line items on the invoice itself.