It actually should leave all of your other session values in tact and just reset the ID. You could store the old Session ID temporarily to use wherever you need it on the page. Something like:
$oldSessionID = session_id();
Then if you need it you can always refer to the old session ID on that page as:
<?php echo($oldSessionID); ?>
and leave the other code on your page on the bottom to clear the rest of the session variables.