What document does DSS publish to change or clarify existing policy requirements in the NISPOM?

The Industrial Security Letter (ISL) is the correct document published by the Defense Security Service (DSS) to change or clarify existing policy requirements in the National Industrial Security Program Operating Manual (NISPOM). ISLs serve as a way to communicate important updates, directives, and information to the industrial community regarding security policies, practices, and procedures. This flexibility allows the DSS to respond quickly to emerging security issues and requirements, ensuring that organizations under NISPOM maintain effective security protocols.

The other documents listed serve different purposes: the Agency Security Directive (ASD) is typically used to modify instructions within a specific agency, while the Security Policy Framework (SPF) provides a broader context for security policy across the government. The Security Classification Guide (SCG) relies specifically on instructions related to the classification of information, rather than policy clarification regarding the NISPOM as a whole.