The U.S. Nuclear Regulatory Commission (NRC) is addressing the human performance aspects of changes to operator actions that are credited for safety, especially those involving changes in the licensing basis of the plant, e.g., using a manual action in place of an automatic action for safety system operations. This document provides guidance for reviewing changes to human actions that are credited for safety. In this document, the term human action and operator action are used synonymously because most of the types of actions discussed are performed by operations staff. The evaluation method uses a two-phase approach. The first phase is a screening analysis of the licensee's proposed modification and the affected human actions to assess their risk importance. A graded, risk-informed approach is used to determine the appropriate level of human factors engineering review. This approach can be accomplished for submittals by licensees that are either risk-informed or non-risk-informed. For a risk-informed submittal, the first phase has four steps: Use of Regulatory Guide 1.174 to determine the risk importance of the entire plant change or modification which involves the human action; a quantification of the risk importance of the human action itself; a qualitative evaluation of the human action; and, an integrated assessment to determine the appropriate level of human factors engineering review. The proposed human actions are assigned to one of three risk levels (high, medium, low) as a result of phase 1. The level of the human factors review in the second phase corresponds to these risk levels. In the second phase, human actions are reviewed using standard criteria in human factors engineering to verify that the proposed action can be reliably performed when required. Human actions in the high risk level receive a detailed human factors engineering review and those in the medium risk level undergo a less detailed one, commensurate with their risk. For human actions placed in the low risk level, there is a minimal human factors review or none. The NRC review of licensee submittals that involve changes to human actions is an iterative process. The final results of the human factors review will provide input to the Integrated Decision- making and to a Safety Evaluation Report.