Really helpful quote from @pictureamoebae about ReShade
You can install ReShade without the assistant (or mediator, if you’re using version 1.0 or 1.1) by first renaming the dll manually. What you rename it to depends on what game you’re playing; for The Sims 4, for example, you rename ReShade64.dll to d3d9.dll.
Then you put that file, along with ReShade.fx and the ReShade folder into the folder where your game’s exe is (again, for TS4 that would be the Bin folder).
To edit the files, all you need is a text editor (I recommend Notepad++ for ease of use and reliability). You open the various .cfg files and edit the lines you want. All the values are the same as what you would see in the assistant/mediator, just written down in text file format. When you save a .cfg file it updates live in game, just as it would if you were using the assistant.
One added bonus of doing it this way is that you can use values that lie outside of the range specified (you can’t when using the assistant/mediator). Some of the best effects can come from using values outside of the official range.
For the longest time, ReShade didn’t have an assistant or mediator program, and this was how you had to use it. It’s the least fussy and most reliable way to use it, because you don’t have to rely on yet another program with yet another awkward and counter-intuitive UI.
ReShade 3.0 will be doing away with the assistant (it’s almost universally hated), and the developer has been looking into an in-game UI approach similar to that used by ENB. You’d still be able to edit files manually (via Notepad++) as well. I’m unsure whether there will still be an installation tool or not, but one isn’t needed in order to use ReShade either way.
Using a text editor to configure ReShade is actually a more foolproof method - I based my tutorial on the helper application because it seemed like a friendlier/less intimidating way for people to dive and get started.
Try this if you have troubles with the program!