Optional Modification definition in Computer Security terms:
Definition(s): National Security Agency (NSA)-approved modification not required for universal implementation by all holders of a COMSEC end-item. This class of modification requires all of the engineering/doctrinal control of mandatory modification but is usually not related to security, safety, TEMPEST, or reliability. See mandatory modification (MAN).
Source(s): CNSSI 4009-2015
reference: CSRC Glossary