I have a button in my invoice record that downloads a file from my dropbox, is it possible to leverage the same script in Invoices in My Account?

In a single word: yes. In two words: it depends. It is very doable to implement on the frontend a button that triggers some script to fire in the backend and then for that return an object such as a file. For example, I wrote this example to add a button to let people download their order history as a CSV file https://developers.suitecommerce.com/add-a-button-to-download-order-history-as-a-csv-file.html

Will take a closer look, definitely appreciate the answer!