If you were able to do so in magic, and then lost your faith, the magic would probably still be working, but if your self-esteem lowered or for example: you did a spell to get thin, and then lost faith, and started eating loads, you wouldn't stay thin.
"It may be impossible to change your physical appearance by glamour magick... But can't you make the outcome temporarily?"
You are contradicting yourself , you say that you know it is impossible to transform physically with glamour spells but then you claim that it is possible to do a glamour spell that transforms you temporarily ?
Also , glamour spells in general do not work at all other than the ones used to change the perception of others .
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.
@DarkSphere Well I meant like I know no such glamour spell can change you permanently. So if you had like brown eyes and you wanted blue.. You did a spell but it's not like it would last forever or some would like it too. What I mean is like, can't glamour spells work temporarily such as for a few hours or a day?