Sorry.
I’ll try explaining it once more.
Backups you make to iCloud right now, with the current iCloud ID, are tied to that ID only. So if you replace it with a different one that already exists, you can’t use those backups any more, because of the new iCloud ID.
It’s the same with photos. iCloud Photo Library, Photo Sharing, and My PhotoStream are tied to one email address/iCloud ID only. When you change the ID, you can’t access them any more on your iPad. They are still available online, btw, when you login to
www.icloud.com on a computer, so you could save them from there. There are a few other features tied to the iCloud ID as well that will disappear, when you change the ID.
For contacts, reminders, notes and calendar events, it’s not necessary to keep the iCloud ID. These are tied to the email address. When you set up the email address of the current iCloud ID after changing the ID on your iPad (not as iCloud ID, but simply as an online account), and you enable them, they will appear on your device again. Just as an example to show what might be used from the current account, if you replace it with a new iCloud ID and add the email address to your accounts(this is from an Outlook account, though):
Hope that helps.
Merry Christmas!