In eZ Publish legacy, via the `eZUser::setInformation()` method, it's possible to update the login field of a given user object. https://github.com/ezsystems/ezpublish-legacy/blob/master/kernel/classes/datatypes/ezuser/ezuser.php#L257-L278

However, in the Platform API, there's no way of doing this. http://apidoc.ez.no/sami/trunk/NS/html/eZ/Publish/API/Repository/UserService.html

To me it seems as though we should probably (by means of a userUpdateStruct?) possess the ability to change the login of a user (assuming that they supploy password).