Append to downloads on product upgrade releases

Build custom module for Zencart that accomplishes the following: Admin orders editor that appends the downloads of existing orders of a specified product (select via dropdown or entering partial information) and a text box to enter the path to the download. Include default Zencart attribute settings that go with Zencart when you add a single product by default to NEW ORDERS. (The difference between this module and what Zencart has for default attributes is this will append all previous orders IN ADDITION to adding to new and future orders.) Provide same buttons and functionality as default attribute downloads except add to provide the above. Appending the existing Zencart GUI for attributes is preferred by adding buttons. Note: I use the Downloads Manager addon module from Zencart that provides more than one download per product and puts downloads into groups. Problem is this module does not fix existing orders. Modification I am asking extends this function to add to existing orders if right information is entered and the "Append" button is clicked.