I have posted up this answer before and then have gotten PMs asking if their case is any different because I answered it on another area and their system maybe different then this one or that one.
There is only one way to Downgrade without a flasher and that is to be on custom firmware and then want to Downgrade the system. This is the only way you can do it. If a system is on ofw and you want custom firmware on it you need a hardware flasher. Thanks.