LiveID phone can be changed without doing a full factory reset.

On the desktop:

  1. Go to the website http://account.live.com and login under the old account [email protected].
  2. Change your Windows Live ID (use any existing account or create a new one [email protected]).
  3. Save the changes and login under the new account [email protected].

On the device:

  1. Use the registry editor to the following modifications:

    [HKCU\Software\Microsoft\ActiveSync\Partners\{B2830118-7BC6-4A74-8C9A-3D8B9CEF88E0}]
    “Email”[email protected]
    “User”[email protected]

    [HKCU\Software\Microsoft\IdentityCRL\Environment\Production]
    “DefaultID”[email protected]

  2. Restart the phone.

All Windows Live ID changed without a full reset!

The ID change can be made using IDswitch

PS: This way you can change only the ID, not the region, because the Microsoft billing information entered during the initial registration.