He wanted to write someone and demand a refund on his dark side which clearly ought to have irresistible magical power but had turned out to be defective.

You couldn't changed history. But you could get it right to start with. Do something differently the FIRST time around.
This whole business with seeking Slytherin's secrets... seemed an awful lot like the sort of thing where, years later, you would look back and say, 'And THAT was where it all started to go wrong.'
And he would wish desperately for the ability to fall back through time and make a different choice.
Wish granted. Now what?

I'm wondering if there's a spell to make lightning flash in the background whenever I make an ominous resolution.

I don't want to rule the universe. I just think it could be more sensibly organised.

I only want power so I can get books.

Textbook science is beautiful! Textbook science is comprehensible, unlike mere fascinating words that can never be truly beautiful. Elementary science textbooks describe simple theories, and simplicity is the core of scientific beauty. Fascinating words have no power, nor yet any meaning, without the math.