HiddenAdmin.ps1

$Account = "admin"
$Key     = "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList"
$Split   = @( )
ForEach ($Node in $Key -Split "\\")
{
    $Split += $Node
    $Path   = $Split -join "\"
    If (!(Test-Path $Path))
    {
        New-Item $Path -ItemType Directory -Verbose
    }
}

Set-ItemProperty -Path $Path -Name $Account -Type DWORD -Value 0 -Verbose