Since the official forums are more dead, I have decided to use GOG where the game was sold at one point.
And because this is the place I know.

This mod alters the game in a very cheaty way, but also simple way.
Such as, but not limited to larger inventory space and addon slots, better aim, twice as good visibility range day and night.
Faster vehicles, more levels (not maps) and faster leveling. And that is just the gist of it all.
If you want a full overview of what was changed from vanilla to this mod, check out the details file.

And here is the cool thing with this mod: You can make changes of your own too. Just look through the files.

Just remember to make the freaking backup of the "gamedata.vfs" file before you do anything, as this mod changes the CORE game.
This mod does not add a file, it CHANGES files within the core game.

The reason for this was simple: Modding support for this game is wonky at best, sometimes the mod would work,
other times the game would not see the file at all.
This way, the game always see the changes and keeps on going.
The downside is the known issue stated below:

Crouching or going Prone cause the game to freeze up with this mod "installed". But that is about it. I have already completed the game twice with my mod, works just fine, so long as i keep my hands from Crouching or going Prone.

Also this mod is meant to be played on IMPOSSIBLE difficulty, as the name implies.

I even made a video showing you how easy it is to install the mod: https://www.youtube.com/watch?v=YN6l4a0D0ck
It's not the best kind of vid, but it's serviceable.

Either you like my mod, or you do not.

If you like some changes be done to the mod, post it here, and i may get back to you... if and when i notice posts.
I don't use gog often.

Can also contact me via Discord: Copper B.#6228