First thing you'll need a hex editor. I use HxD, since it's free and it works. You'll also need to find your save files. On my end they were at this location:

C:\Program Files (x86)\Steam\userdata\[userID]\1088710\remote

It should be the same for you, hopefully. Here you'll find a lot of files named savegame1.sav, savegame2.sav, etc. These correspond to saves in the game - so on the load screen when you see 01, that refers to savegame1, 02 = savegame2, etc.

Open up the save file that corresponds to your latest save in HxD. In most cases this is the savefile with the highest number, since that's the most recent one - unless you have overwritten a save.



I attached the image above which should show something similar to what you should see. The highlighted bytes - at 04-05 on the 00000010 offset - correspond to the difficulty.

00 00 = Easy

01 01 = Medium

02 02 = Hard

03 03 = Ex-Hard

This helps you start a new game on ex-hard or help you change your difficulty mid game so you don't have to restart a playthrough