One can apply (multiple)master pages to all pages and you can alter them within any page that uses that master page,
Wouldn't it be a good idea to have a context menu option or a button or ungroup option in the layers panel to make an applied mp become local?
Now the adding>duplicate objects>dragging them out the mp-group in the layers panel seems a bit cumbersome,workable but cumbersome.
Not all is lost since one can re-apply mp's after clearing it from a certain page
And vice versa:promote page to master page