I have a very specific issue where I need to be able to add watermarks to Keynote, but with the ability to change the watermark for each person/version who will have access to the Keynote (that is, their name would appear on another different version).
Is that even possible? (App or automatic functions)
I would keep a separate Keynote document that has just the rotated Shape with boilerplate text in it (e.g. draft), and select, copy, and paste that into the Keynote document that requires a watermark. Then center it and add the intended watermark text, and then from the Arrange panel, send it behind your existing Keynote content.
Keynote does not have an inbuilt tool to automatically create "text watermarks"
All you have to do for text, is add a text box on the slide and enter the required text.
Fast, auto, watermark to keynote solution
