Composer page attached to User 5.6.2.1

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Hoping someone can help here. I have over 200 Vendor pages setup through Composer (Dashboard Page Manager). First what I need is to assign a list of Users (each to a Vendor page). There is a custom attribute in the Vendor pages that contain the Users email address. This is a rebuild of an existing site and we need to assign them to their page so they can edit.

What I ultimately need is that when a Vendor signs up, they are given access to a new Vendor page that they and the Admin can edit once they are approved.

I am hoping this is something can be automated, possible?