The Secretary of Defense shall by regulation establish programs which provide domestic business concerns an opportunity to purchase or borrow replenishment parts from the United States for the purpose of design replication or modification, to be used by such concerns in the submission of subsequent offers to sell the same or like parts to the United States. Nothing in this section limits the authority of the head of an agency to impose restrictions on such a program related to national security considerations, inventory needs of the United States, the improbability of future purchases of the same or like parts, or any additional restriction otherwise required by law.