The most appropriate method to address this business requirement is to extend the existing shipping logic in the shippingMethod.js file within a custom cartridge. This approach involves utilizing the module super pattern to extend existing functionality rather than rewriting it entirely. The extension should include logic to check the category of the product and apply an exception for the specified brand (XyzTV) during the promotion period. By leveraging the module.superModule, developers can invoke the original method's functionality and seamlessly integrate custom logic, ensuring maintainability and adherence to best practices in customization within the Salesforce B2C Commerce environment. This is aligned with Salesforce's recommended approach to extending and customizing core functionalities in a scalable and upgrade-safe manner.