[Kazun]

Код:

Get-ADComputer -Filter "extensionAttribute1 -like '*'" -Properties extensionAttribute1,extensionAttribute2 | Group-Object extensionAttribute1 | Foreach {
	$ex2 = $_.Group | Where {$_.extensionAttribute2 -match "^\d{3}$"} | Foreach-Object {$_.extensionAttribute2}
	$start = 0
	$id = "$start".PadLeft(3,'0')
	$_.Group | Where {$_.extensionAttribute2 -notmatch "^\d{3}$"} | Foreach-Object {
		do {
		    $start++
		    $id = "$start".PadLeft(3,'0')
		} while($ex2 -contains $id)
		Set-ADComputer $_ -Replace @{extensionAttribute2=$id}
	}
}