I'm creating an interactive pdf where you can click on different elements and get more information via a pop up box (a group of shape, text, etc)
There's going to be several per page.
I'm hoping I can somehow create these button shells on the master and just change the text content on the pages themselves, but it seems I can't edit the text on the page if it was created in the master.
An alternative format to PDF is HTML5. Have a look at InDesign's Publish Online; you can produce documents with the kind of interactivity you want, the only disadvantage is the user has to be online and you can't monetise the content. The other possibility is in5, an InDesign plugin (at extra cost).