As an experienced full-stack developer, I understand the value of time in a project as crucial as yours. My expertise lies not just in WordPress and Shopify but also in HTML, JavaScript, MySQL, and PHP - the skills that are pivotal in creating the Sonic Panel Clientexec modules you are looking for. I have gone through the API documentation and feel confident that I can efficiently build the functions you need like create, changepass, terminate, suspend, and unsuspend using the built-in API.
Furthermore, my penchant for detail and thoroughness ensures that not only will I create these modules for you but also explain their workings if needed. This will be valuable not just for your immediate requirement but can even lead to a long-term partnership as you have mentioned about having more products and modules to create.
Lastly, I take user experience seriously. Therefore, all the solutions I provide will encompass cross-browser/platform compatibility as well as mobile-friendly interfaces to make sure it caters to all your customers' needs. With my deep understanding of WordPress Development and e-commerce systems like Shopify, along with a commitment to optimal performance, I believe I would be a perfect fit for this job.