Right, glamour spells can only change how people see you.
I think belief is a big part of magic so if you stopped believing that it worked, your spells would lose power. Maybe not all of it, since you apparently believed when you cast it.
As for temporary, absolutely. Just say when you want it to stop sometime in the spell, or make a charm, poppet or something physical that you can easily take apart to undo the spell when you're ready.