I think there may have been some misunderstanding here. That part was about the Image Occlusion Enhance add-on, not native Image Occlusion. I was explaining how to apply changes made in one note to all its “sibling notes”.
(On a side note, you can decide which fields do and do not get overwritten when using Edit Image Occlusion -> Edit Cards by changing IOE’s configuration.)
I don’t think there is an easy way to do that at the moment. As mentioned previously, native Image Occlusion is still quite new and some of its functionalities are a bit simplistic, especially if you are used to Image Occlusion Enhanced.
I think the best way to delete masks, currently, is to select them with the mouse, and then click on the Trash Bin icon or press Del on your keyboard.