Changing your level is a bad idea, as several important story events / points are based on it. e.g. from memory: defeating the Big Bad (at that time) in the chapter 3 (?) war has a spread of points assigned to it, where being totally underlevelled (i.e. you 1000% cheated) gives none, and being overlevelled gives only +1 vrs like +3 for the perfect level range. This is enough of a difference to prevent you from two S-tier outcomes from that chapter, as you need to pull points from elsewhere to cover for it.
The level / xp curve in this game is TIGHTLY controlled and monitored (something that that person complaining failed to notice) - basically, only ever alter stats or money (and, again... be careful. e.g. cheating infinite pr0n and unlocking the mines in chapter 1 (300k? ish) is a bad idea because the game now knows you've cheated, and there's repercussions).
As for the mechanics of your question - it's most likely you're merely altering active memory (which is what cheat engine does) without writing it to the save. As you're on android and playing through a 3rd party program, no idea. Suggested search terms: "joiplay memory editing save state"