If you gave me the fix for it then I used it.
I actually don't think storing the old stats is necessary (except the level).
The Third Eye automatically reverts the one stat it changes back to the original once it's removed, if it can do it for Evade it should be able to do it for level.
Let's say the accessory makes you level 50, when you take it off and it puts you back to 25 the game will notice those aren't level 25 stats and lower them (though most likely only at next level up) at least that's what happens when you give a character starting stats higher than what they should have at that level.