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.