Figured out what needed to be changed to work in 4.7.6+ in case anybody else runs into this.
Replace:
Code:
db_query("UPDATE xcart_orders SET status='C', tracking='$comments' WHERE orderid='". $result_ordercheck['orderid'] ."'");
WITH:
Code:
db_query("UPDATE xcart_orders SET status='C' WHERE orderid='". $result_ordercheck['orderid'] ."'");
db_query("INSERT INTO xcart_order_tracking_numbers (orderid, tracking) VALUES ('". $result_ordercheck['orderid'] ."', '$comments')");