This script will take the IdentifyingNumber from the WMI and will change the TS value according to the Service Tag (IdentifyingNumber).
Read how to pace it in the Task sequence .
#===========
$Progress.CloseProgressDialog()
$TSEnv = New-Object -COMObject Microsoft.SMS.TSEnvironment
$tag = gwmi win32_computersystemproduct | select -ExpandProperty IdentifyingNumber
if ($Tag -like '*XX*') {$TSEnv.Value("OSDDomainOUName")='LDAP://OU=XXXXXX,DC=ecitele,DC=com'}
elseif ($Tag -like '*YY*') {$TSEnv.Value("OSDDomainOUName")='LDAP://OU=YYYYY,DC=ecitele,DC=com'}
#===============