Hi,
Thank you for posting your query in Microsoft Community.
From your description, I understand that you are unable to download apps, receiving an error: "We're sorry, something went wrong. Your account wasn't changed to this Microsoft account. Code: 0x80070426". I will be glad to assist you.
I would suggest you to run the Microsoft Accounts Troubleshooter and update us on the status of the issue.
http://go.microsoft.com/fwlink/?LinkId=268424
For any Windows related issues please feel free to contact us and we will be glad to help.