User can add up to 3 portals address. End user can be in any of those portals. But you need to provide customer which portal to select from Login screen. No server or client side configuration required.
Now you can provide 3 different services to same user.
Let's say you are using Portal 1 for Live TV with VODs and no Series (Portal is running fromd different Server). And you are using Portal 2 for Live TV, VODs and Series (Portal is running fromd different Server).
Example
You can show/hide TV, EPG, VODs, Series, Multi-screen, etc buttons for each portal.
You don't need to make any client or server side changes.