@Marina_Corrales one can now set a password and then change the account email via Settings > My account. Though this enables signing in with the new email and chosen password, at the moment the account still remains associated to the old Gmail and its Google Drive.
The ability to fully switch will finally be implemented over the coming weeks (by November at the latest); in the meantime attached files remain safe on our S3 servers and accessible via the library. We will send out a general communication once the feature is released.
Separately, it is worth noting that the limitations when citing in GDocs while signed in to multiple accounts on the browser stem from privacy limitations imposed by Google — their API gives no control over which account executes formatting commands (script requests). We recommend the use of Chrome Profiles to keep account activity separate. As long as the Paperpile-associated account has editing access to the document, formatting should run smoothly.