Set AD Group ACL

Set-ADGroupACL.ps1

$GroupObject = Get-ADGroup 'MyGroupName'
$NTPrincipal = Get-ADUser 'myUserName'

if ($GroupObject -and $NTPrincipal) {

    $acl = Get-Acl "AD:$($GroupObject.distinguishedName)"

    $identity = [System.Security.Principal.IdentityReference] $NTPrincipal.SID

    $adRights = [System.DirectoryServices.ActiveDirectoryRights]::WriteProperty -bor [System.DirectoryServices.ActiveDirectoryRights]::WriteDacl

    $type = [System.Security.AccessControl.AccessControlType] "Allow"

    $inheritanceType = [System.DirectoryServices.ActiveDirectorySecurityInheritance]::None

    $ACE = New-Object System.DirectoryServices.ActiveDirectoryAccessRule $identity,$adRights,$type,$inheritanceType

    $acl.AddAccessRule($ace)
    Set-Acl -AclObject $acl -Path "AD:$($GroupObject.distinguishedName)"
}