Private/Win/Set-UnattendedWindowsAdministratorName.ps1

function Set-UnattendedWindowsAdministratorName
{
    param (
        [Parameter(Mandatory = $true)]
        [string]$Name
    )
    
    $shellNode = $script:un |
    Select-Xml -XPath '//un:settings[@pass = "oobeSystem"]/un:component[@name = "Microsoft-Windows-Shell-Setup"]' -Namespace $ns |
    Select-Object -ExpandProperty Node
    
    $shellNode.UserAccounts.LocalAccounts.LocalAccount.Name = $Name
    $shellNode.UserAccounts.LocalAccounts.LocalAccount.DisplayName = $Name
}