I don't want to hit another button bacter, i prefer rejetto's initial proposal of it listening for saves on the external file, so basically hfs will read its template from an external file, instead of the editor, there is no point in complicating things, it just confuses the interface and gives rejetto more work to do.
I cant say i'm very concerned with diff.templates, i am yet to use one, so i am going to assume mars' idea there is having the same effect for diff.templates, making HFS read an external file.