Switching accounts linked to Apple ID

Had an old account linked to my Apple ID that was no longer in use and have been playing a new account, unlinked to game centre and just linked to the webstore on a different email, for the last year. Now upgrading my phone and I'd like the new account on my Apple ID. I can't create a new Apple ID with the webstore linked email because too much is tied to the current one. I couldn't find a way to do it in game and wondered if there was a way at all.

Thanks!