Which of the following modifications cannot be made using membership add-ons?

The correct choice is based on understanding the limitations of modifications allowed under membership add-ons. Membership add-ons are typically designed to enhance the existing membership but do not include structural changes to the membership itself.

In this case, extending the duration of the membership is a fundamental alteration to the agreement and the terms of service, which falls outside the scope of what add-ons can influence. Membership add-ons primarily focus on enhancing or providing additional benefits and services to the existing plan rather than redefining the core terms such as duration.

On the other hand, options like adding additional services, increasing the membership price, and updating customer account details are actions that align with the purpose of membership add-ons. These are enhancements or modifications that add value to the membership without altering its fundamental structure.