If an existing Member purchased into a separate membership if they use the same email, then they would cancel their old subscription and would belong to the new membership. If they use a new email and have 2 separate accounts, then they would have 2 separate logins and see separate things in each members area.
Yes, things do change. A landing page does not have the code for sending the form, so any forms on the page may not send and/or may not be setup properly if the page is not marked as a capture page.
A. By default the members area is the same.
But, we can customize it as needed to look different from the other members area.
They would still login at the same place, but we can have different headers, etc for the members area for Members in the new membership.
Yes, you can edit the contents of any page in your members area through the file manager
From the file manager go to the uploads/adminpages folder (there is a quick link in the top right).
There you will see html versions of all the php pages in your system's members area which you can edit to change the appearance of the php pages in your software members area.