Who created reshade? Maybe they can make something that could counter this.
ReShade is just one 3rd party shader program. Even if you found a way to prevent people from using it, there are others.
I just did some more tests on my own. The only way to prevent people from seeing in the dark with 3rd party shaders is to make
everything literally (0, 0, 0) RGB black. (I.e. make shadow color black and move the sun below the ground.) Because black is black and making black brighter is pointless when everything is black. But if everything is black then
nobody can obviously see anything without using lights, which defeats the purpose of being stealthy. If anything in the scene is not (0, 0, 0) black, I can bring out even a 1 point color variation so the difference is like day and night. In other words, there is nothing you can do. If people want to cheat by seeing in the dark, they can.