I;m sorry, I missed that this was for the User Registration solution pack.
To get the user registration solution pack to email the unencrypted password, you wont use the security Assist email password behavior, you will just need to modify the WA_UniveresalEmail/Email_Templates/Lostpassword.php page.
Change:
<?php echo($row_LostPW['UserPassword']); ?>
to:
<?php echo($_SESSION['NewPW']); ?>