The Edit Window Seems Locked, How Can I Edit that Layout?
When you arrive at the Edit Appointment mini window during the creation or edit of an appointment, you're visiting the layout inside of a paused script. Accordingly, you can't enter layout more, or do much of anything, until you leave the screen.
So, if you want to edit this layout you have to enter layout mode from one of the other screens, like the Daily View. Run the "Show Status Area" script first so that you can see the tools in the left hand status area and then enter layout mode. Once there you can use the layout list (a little pill of a button towards the top of the status area below the "pencil" icon) to scroll to the "Mini Window Edit Appointment" layout. Once there you can edit the layout as if it were any other FileMaker Pro Layout.