I think there are ways to inject cheats on to saves, then use save mounter. I saw one for one of the final fantasy games. you can even use it on official firmware (latest) with save wizard. you just need to get the save into a decrypted state. however, I don't know if there are any save managers for that game.
I really suggest not to cheat in social links in this game, you will break the game if you level up some of the people not legit way, you have enough data to level up the important people, if you playing royal, just make sure you level up akitchi to 8, maruki to 9 and kasumi to 5 before November.
But if you mean the knowledge and other stats you can cheat in them no problem.
They are not hard.