UpdateImmutableID

 $usersTable = New-Object system.Data.DataTable “UsersTable”
 $column1 = New-Object System.Data.DataColumn userPrincipalName,
 ([String])
 $column2 = New-Object System.Data.DataColumn immutableId,
 ([String])
 $usersTable.Columns.Add($column1)
 $usersTable.Columns.Add($column2)
 $users=Import-Csv -Path users.csv -Header “userSamAccountName”
 foreach($user in $users)
 {
 $adUser = Get-ADUser -Identity $user.userSamAccountName
 $adUserGuid = $adUser.ObjectGUID
 $byteArray = $adUserGuid.ToByteArray()
 $immutableId = “”
 $immutableId = [system.convert]::ToBase64String($byteArray)
 $row = $usersTable.NewRow()
 $row.userPrincipalName = $adUser.userPrincipalName
 $row.immutableId = $immutableId
 $usersTable.Rows.Add($row)
 }
 $usersTable | Export-Csv “c:\Users\Inlogic\UserExportIds.csv”