I would like to add a shortcut for "always use pressure for Opacity and Size", but before investing time reasearching the api and how to do it, I would like to know if it is possible.
I do not think it would be possible. There are no entry in edit shortcuts for the UI element and using them show them to be events that are not recorded by the scriptlistener. Without the source for Photoshop there is no way I know to get at Photoshop UI. Their UI element are not even on screen all the time and their locations can change.