Oh I see.
The reusable elements are kind of on lock down - when viewed from any regular page in the editor.
But if you click on “Signup / Login Popup” (from the drop down in your screenshot) - and then click again on the primary container (ie. your reusable element) - you will be able to change the Title there.
Is that what you are trying to do?
As it sits now - reusable element can only have a singular name.
So for example; if you have “page1” and “page2”
You can not have “page1Signup” and “page2Signup” if they are both the same reusable element - you have to just refer to the reusable element with a general name.
I think I am starting to understand from your perceptive