The approval needed to replace a Stage Plan with an Exception Plan must come from the Project Board. This is because the Exception Plan is created when a Stage Plan is forecast to exceed its tolerance levels, and the Project Board is responsible for approving such significant changes in the project's direction or management.
References: PRINCE2 Foundation official documentation and study materials.

The Project Product Description is a key document in the PRINCE2 methodology that outlines the purpose, composition, derivation, and acceptance criteria of the project's main deliverable. It is crucial for defining what the project needs to deliver to be considered successful and to receive formal acceptance. References:
PRINCE2Foundation Training Manual; PRINCE22017 Foundation handbook.

Risk tolerance is defined as the measurable threshold that represents the tolerable range of outcomes for each objective at risk. It quantifies the level of exposure to risk that an organization or project can withstand, helping to guide risk response planning and risk management strategies.
(PRINCE2 7 Foundation Handbook, AXELOS)

Risk response refers to the actions identified and implemented to bring the risk exposure to an acceptable level. These actions are part of the risk management process and aim to reduce, avoid, transfer, or accept risks depending on their potential impact on the project. References: PRINCE2 Foundation Training Manual; PRINCE2 2017 Foundation handbook.

The purpose of the Risk theme in PRINCE2 is to establish a cost-effective procedure to identify, assess, and control the uncertainties or risks that can affect the achievement of project objectives. This involves understanding how risks can impact the project and managing them proactively to ensure project success.
References: PRINCE2 Foundation Training Manual; PRINCE2 2017 Foundation handbook.