If it's just higher difficulty you're after and none of the available hacks are what you're looking for, keep in mind that back in the days before ROM hacks existed, people still managed to do their own challenge playthroughs without needing to hack anything, and that is still an option for you today - you're limited only by your imagination! As examples, choosing to never upgrade your equipment or to fight without equipment at all would definitely make the game more challenging. Have you ever tried a solo-Cecil playthrough? What about a girl-only or boy-only playthrough? How about a no-magic, only-magic, or low-level playthrough? Having Cecil at level 1 deal the killing blow to Zeromus is pretty funny. For pure masochism, only fight enemies when you're afflicted by the tiny/pig/frog statuses, and only with physical attacks.