user behavior: global object to apply to each page -or- custom object

I have a site that allows users to create and share lists. Each page represents a different list. Next, I add a secondary list that represents a shared or global list on all user pages. Although this secondary list is global, I want the user to have the ability to create a customized variant that is not global.

Basically, I maintain a unique global list that can be edited on any page, but you can disable the global aspect page by page.

How could you put this?

This is what I have:

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