The reason I ask this is I wanna make the title of the Byzantine Emperor "Autokrator" because it sounds really cool :happy:.
Yes, go to Crusader Kings II/localization/text1.csv, open it with Wordpad or Notepad. Then look for this line
emperor_greek;Basileus;Basileus;Basileus;;Basileus;;;;;;;;;x
And change it to this
emperor_greek;Autokrator;Basileus;Basileus;;Basileus;;;;;;;;;x
And then save the file as a .csv-file again.