Use of a ``memorandum of understanding,'' which purports to modify mandatory FAR and HHSAR provisions to make them acceptable to a prospective contractor, is not authorized because it may address matters contrary to the language of the solicitation or prospective contract. A memorandum of understanding does not bind the Government under the contract. The Contracting Officer shall make a change in a solicitation or contract only by amendment or modification, respectively. When a change to a prescribed contract clause is considered necessary, the Contracting Officer shall request a deviation.