Continuing to add support for keyboard shortcuts in Omnifocus, I’ve added a new plugin called “Toggle ‘Complete with last action'” to my Github repo. It takes a selection of tasks or projects, and for any that have children (i.e. either projects or task groups) it toggles the checkbox for “Complete with last action”.
I couldn’t find a keyboard shortcut or menu item for this, but if you know of one let me know. This seems like it should be unnecessary.