Thank you very much for your patience.
Thank you for writing. The format cell dialog window is a part of the toolbar which communicates with pivot via API methods (https://www.flexmonster.com/api/). Please note that we provide the source code of the toolbar, it means that you can reuse and rewrite it the way you want. Also, if you need to make your custom toolbar this article may help you – https://www.flexmonster.com/doc/customizing-toolbar/. Our component allows making your own custom toolbar based on our standard toolbar with the custom tabs, new icons, and functionality.
Please let us know if the information above was helpful for you.