I would expect the "Add" button to ask me for a name for the new rule file, and
then add it to the list of commands (in the selected category), and perhaps
immediately open it in the editor. Instead it opens a filechooser (do you need
to have an existing rule file somewhere?), which is not consistent with the
behavior of any similar manager dialog I can think of. Should perhaps also be
called "New". Or if there is a reason to add rules that are saved on disk
somewhere, at least "Add" should open a simple dialog with radio buttons:

(*) Create new rule file
    Name:     [____________________________]
( ) Add existing rule file
    Location: [________________] [Browse...]