The most effective method to prevent the recurrence of configuration mistakes is to implement a formal change control process. FortiManager's workflow mode is designed for this exact purpose. By enabling a workflow, changes made by an administrator must be submitted for review and explicitly approved by another, typically more senior, administrator before they can be installed onto a FortiGate. This mandatory review step provides a crucial checkpoint to catch potential errors, enforce best practices, and ensure configuration integrity, directly addressing the need to prevent repeated mistakes.

A. A TCL script is a custom automation tool. While it could validate a specific known mistake, it is not a comprehensive solution for preventing various potential human errors and lacks the oversight of a formal review process.
B. Restricting access to revision history is counterproductive. It removes the ability to audit past changes and learn from them, and it does nothing to prevent an administrator from making a new mistake.
C. Requiring a change note is a good documentation practice for accountability and auditing. However, it does not prevent an administrator from saving and installing an incorrect configuration.

1. FortiManager Administration Guide 7.4.1, Page 103, "Workspace and Workflow" section: "When workflow mode is enabled, administrators must create a new session, make changes, and submit the changes for approval. A senior administrator can then review the changes and approve or reject them. After the changes are approved, the administrator can install the changes to the managed device." This directly supports the use of a workflow for review and approval to prevent errors.

2. FortiManager Administration Guide 7.4.1, Page 104, "Workflow mode" section: "Workflow mode is a feature that allows you to create a workflow for device configuration and policy changes... This allows you to control changes in your network." This highlights that the feature's primary purpose is to control changes, which is central to preventing mistakes.