Heelo Mike,
Yes, you can generate reference numbers automatically. Just add something like this in your code, in the files front.offer_save.php and admin.offer_save.php.
if (!$offer->store()) {
echo "<script> alert('".$offer->getError()."'); window.history.go(-1); </script>\n";
exit();
}
if ( $offer->reference == '' ) $offer->reference = 'HR'.$offer->id;
$offer->store();
$offer->checkin();
Regards,
Author