# Add New Registry Key
$regHive='REGISTRY::HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU'
$keyname='NoAutoRebootWithLoggedOnUsers'
$value=1
Set-ItemProperty -Path $regHive -Name $keyname -value $value

# Validation
Get-ItemProperty $regHive -name $keyname

PS C:\WINDOWS\system32> Get-ItemProperty $regHive -name $keyname


NoAutoRebootWithLoggedOnUsers : 1
PSPath                        : Microsoft.PowerShell.Core\Registry::HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpd
                                ate\AU
PSParentPath                  : Microsoft.PowerShell.Core\Registry::HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpd
                                ate
PSChildName                   : AU
PSProvider                    : Microsoft.PowerShell.Core\Registry