Rename local user account http://stackoverflow.com/questions/5188917/powershells-script-to-re-name-local-guest-administrator-account

gistfile1.ps1

$user = Get-WMIObject Win32_UserAccount -Filter "Name='$oldName'"
$result = $user.Rename($newName)

if ($result.ReturnValue -eq 0) {
  return $user
  # you may just print a message here
}