Although!
There is most likely a mod out there that you can get with a little searching... if you are on pc.
I'm not sure if there's any mods that will let you be Emperor...at least none that I've come across. Servant of the Dawn will let you become High Chancellor if you play your cards right (and are willing to take the evil path, since it's a post-MQ Mythic Dawn faction mod). Which is basically as good as being the Emperor, considering how things stand at the end of the MQ.
@HeroofKvatch: Orrr you could round up an army, stage an overthrow of a crumbling empire, declare yourself the new Emperor and off anyone who disagrees with you about it.
Spoiler What? It worked for http://www.uesp.net/wiki/Lore:Titus_Mede#Titus_Mede