User blog comment:Omega natsu2/Chapter 413: The Book of E.N.D., Predictions./@comment-9595671-20141211045655/@comment-7418318-20141211111509

No I don't want that. I don't even want to think about the Failbringer arc and any similarity is coincidental and superficial. :P

Even inserting yourself perfectly into the knowledge of the past should still leave these faked memories without little or no emotion and thus with a flaw that can be noticed and used to escape the manipulation. With the whole power of feelings thing going in FT, that seems an appropriate way out, if one is needed.

Or maybe have it be less efficient the stronger someone's will is or the more experience they have. Manipulating the minds of children is likely easier than doing the same to adults, just like influencing children is easier in reality.

But with Grandeeney being described as a very kind a just personality, I think we can trust her not to abuse this power, even if it turned out to be theoretically overpowered.