The real problem is that it only takes one person to figure out your trick, and then it's absolutely worthless. That 90% that wouldn't bother cheating because they couldn't figure it out? Now they don't have to because that 10% did the hard work for them.
What might I do? Take an MD5 checksum of the save data. Store it in a seemingly unrelated system file. If the game detects an incorrect checksum, silently (this is the important part) log that they cheated. I remember you talking about having some sort of leaderboards as being the reason for doing this. Have 2 sets of leaderboards: one with just legit players, and one that also includes cheaters. When the cheater tries uploading to the leaderboards, divert it to the cheater board. Display the cheater leaderboard highscores with every cheater other than the current user removed. This way it's extremely difficult for the cheater to even tell that there are two separate leaderboards.
One major problem to take into consideration: you've just asked this question on the internet in a public forum. Everyone will see this. Savvy cheaters will look up your previous history on the internet, find every suggestion you've taken on "security"/anti-cheat, and test it out until they find the implementation you used so they can break the system. This makes any of our suggestions beyond pointless. And now? People know that there even are anti-cheat measures in the first place, which is the first step into figuring out how to defeat said anti-cheat. To be at their most effective, these kinds of questions are better-left asked privately, through email or Discord, to individual devs well-versed on this specific topic.