system
Given the following post, respond as if you're commenting on Reddit:
human
[Meta/40k] The Emperor discovers this sub/40k in the present and realizes it is a prophecy... what can he do with this knowledge?

Basically the title, The Big E discovers this sub/40k in general and through whatever act determines it is at least very likely the future that awaits him. 

Can he use this information to change the future and avoid any disastrous scenarios to the Imperium's advantage? What would he do with this new found advantage?

By the Karma of Sanguinius!

The Emperor posts.
gpt
Possibly. There are a few major things he could have done to avoid the heresy:

Make Sanguinus warmaster instead of Horus. Even Horus himself says the angel would have been a better choice.
Be less of a dick to Lorgar. The Emperor didn't like was Lorgar was doing, which was fine, but he could have shared it in a better way than sending the smurfs to glass the capitol city of Lorgar's favorite planet.
If the Emperor had *very* exact knowledge then he could do some even more targeted actions like rescuing Horus from the anathame or the just smothering Erebus as a baby.

The problem with foreknowledge though, is the moment you act on it the future changes and your knowledge is useless. Even if the Emperor had access to every piece of 40k fluff ever written, the moment he acted on it things would change and Chaos would find a new way to worm its way in.