The objective of the Closing a Project process in PRINCE2 includes reviewing the performance of the project against its baseline. This ensures that all objectives have been achieved, the project has delivered the required products, and stakeholders are satisfied with the outcomes. It provides a formal closure to the project by ensuring all project work is completed and assessed. References: PRINCE2 Foundation manual, PRINCE2 official resources

The role of the change authority in PRINCE2 is to authorize changes within the project that do not exceed a predefined budget. This role is designated to ensure that any change proposals are evaluated and approved without exceeding the allocated budget for changes, thereby maintaining control over project costs and scope.
PRINCE2 Foundation Manual

According to the 'defined roles and responsibilities' principle in PRINCE2, three categories of stakeholder interest need to be represented in the project management team: business (represented by the Executive), user (represented by the Senior User), and supplier (represented by the Senior Supplier). This ensures that the key perspectives on the project's outputs, outcomes, and processes are fully integrated into decision-making and governance structures.
PRINCE2 Foundation Manual

PRINCE2 ensures that the specific management needs of an organization are met by incorporating tailoring.
Tailoring involves adapting the method to suit the project's environment, size, complexity, importance, capability, and risk. It allows organizations to apply PRINCE2 effectively across different types of projects and organizational environments.
PRINCE2 Foundation Manual

The Project Brief is created during the Starting up a Project process. It defines and confirms the scope of the project, providing a foundation for the Initiation Stage and ensuring that all project stakeholders have a clear understanding of the project's objectives and scope. References: PRINCE2 Foundation Training Manual; PRINCE2 2017 Foundation handbook.