We are [slowly] migrating to using managed AppleIDs. BEFORE you switch away from your old one:
- Fire up Notability
 - Switch to Settings
 - Select iCloud
 - TURN IT OFF
 - Select “Keep on my iPad”
 - Switch to Autobackup.
 - Make ABSOLUTELY certain your files are backing up to Google Drive
- If they aren’t, set that up RIGHT NOW
 
 - Swipe out of Notability
 - Settings –> Sign into your Managed AppleID.
 
This will keep you from losing all of your Notability notes when you switch.