(a) Executions may be levied by the officers to whom such executions are directed or by other officers who are authorized by law to act in their place.
(b) Any levying officer to whom there have been directed two or more executions against a defendant or to whom there have been directed two or more in rem executions against the same unreturned property may aggregate such executions and may make a levy for the total amount due as in the case of single execution.