As William mentioned, Fish must be ready to breed. If the female is not conditioned you will just be wasting your time and not to mention this can bring on stress and not to mention bring on ick if temp goes too low.
Cories are very easy to stress out if water temps drop to fast and they are prone to shock if the PH changes dramaticly.
I have had a few go belly up due to ph jump.
Before you ajust temp I would assure that the female is plump and full of eggs. Just ajusting temp is useless unless they are fully good and ready.
Danny