1) Download a memory editor. This guide will assume you're using Cheat Engine.
http://www.cheatengine.org/

2) Run MGS5, go out into the world, minimize the window.

3) Run Cheat Engine, and load the MGSVTPP process in.

4) Scan type "Bigger than" value "1" hit the First Scan button. Wait.

5) Back in the game, find a single guard out in the world. Heatshot him cleanly.

6) In Cheat Engine, Scan type "Increased value by" value "60", hit the Scan Next button. This will locate where your demon points are being stored in memory. You may find multiple memory locations. In this case, headshot another soldier, then scan next another 60. Repeat until you have one* (or two values, see below)

7) Edit your demon points. Setting them to something small like 5 will restore you to non-bloody once you return to Mother Base.


** After the latest patch, there seem to be two memory locations tracking your demon points. One seems to be for the current sorte or playsession, and the larger number is how many demon points you have total. You'll want to edit the larger number.