I have a wordpress project installed, which came from another user who uses ACF Pro. He use flexible Groups with a wysiwyg editor in it. I have to add a Field to add <sup></sup>. It seems everything is setup with json. I found the json file, but how can I extend the editor with a new field. I also tried to hook into the filter, but it does not changed the editor. What is the right way? To do it in Json or in Functions.php with the hook?