Rename User Account Folder in Windows 10 Preview

10/5/2018 - This issue is updated by the arrival of a Shawn Brink tutorial for how to safely Change Name of User Profile Folder in Windows 10 - User Accounts Tutorials.

Previously this could cause catastrophic failure only recovered this way:

To change a Local Account name follow How to Rename a Windows 10 Local User Account .

For a MS Account follow How to change your account name on the Windows 10 sign-in screen..  You can also change the MS Account to a Local Account and choose any name for it you want.

This will not change the User folder name in Explorer.  The only way to achieve this is to Create a New Local User Account or reinstall.  Do not use ANY method to change the Explorer User folder name in Windows 10 because this can result in a catastrophic failure start loop at the Lock Screen. 

While the User Account name can be changed in Settings, one cannot change the User folder name in Windows 10 without reinstalling.  Any attempt using Regedit to change Profile Image Path in registry will cause a failure to start loop at the Lock Screen. 

To recover from loop try System Restore from Advanced Startup Options in Windows 10 which should be available by pressing Cntrl Alt Del keys at the lock screen, then from the Power icon in bottom right corner of options screen choose Restart while holding the Shift key.  This will boot into Advanced Startup Options where you can choose Advanced Troubleshoot Options for System Restore, of if necessary the Command Prompt.   

If System Restore is not working then from Command Prompt you can patiently try to reverse the registry change following these steps for How to Edit the Registry Offline Using Windows Recovery Environment? - The Winhelponline Blog which should work if followed correctly.  Ask back here if you need any help.