As an experienced web developer with a specific proficiency in HTML, JavaScript, and WordPress, I am well-equipped to tackle your project effectively. Your request for a popup confirmation during the registration process is well within my skill set. I can seamlessly integrate a feature that presents users with a customizable HTML text in a popup along with accept and cancel buttons. If users agree through the accept button, the registration process will continue; if they click cancel, it won't affect the ongoing session.
Moreover, your concern about documentation and guidance isn't a problem either. I understand how important it is for you to have detailed explanations of the changes made so that you can accurately replicate them on your production server. I always create thorough documentation for all my tasks and ensure that my clients are properly guided throughout the process.
Finally, let's not forget the value of long-term relationships you mentioned in your description. I wholeheartedly share your belief in building sustaining connections with clients. Hence, if selected, not only will you receive timely completion of the task, but I'll also be available for any future assistance you may need to enhance your WooCommerce platform. Let me turn this project into a strong relationship!