https://github.com/marvinlehmann/CoD-SCZ-FoV-Changer

CoD.SCZ.FoV.Changer is a minimal open-source GUI tool developed by marvinlehmann for Field of View configuration in the mainline Call of Duty games published between 2008 and 2011 (World At War, Modern Warfare 2, Black Ops One, and Modern Warfare 3). This tool is the easiest method to making on-the-fly configuration changes. I take no credit for their work; I simply wish to pay my respects by sharing this excellent program.

For the sake of brevity, this guide will omit information already covered in xFaNaTiix's Guide on FoV.Changer. Their guide can be found here:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?l=english&id=456437018
Do not use both methods for any singular game. You can use either the Launcher Method or Parallel Launch method for each game. For example: Launcher ONLY for World at War and Black Ops while Parallel ONLY for Modern Warfare 2 and Modern Warfare 3. You will open duplicate instances of FoV.Changer if you use both methods.

As of now, this guide only supports WinOS. There are two known methods for WinOS. Any information regarding Linux-based Operating Systems would be greatly appreciated.

This method is less complex but is slower on a per-launch basis. Ideal if you have two or more of the applicable titles.

Navigate to the launcher's location in File Explorer and copy the path address.
e.g. "Downloads/" if you just downloaded the .exe
(You can use "Ctrl+L" to select the address bar, "Ctrl+A" to select the entire address, and "Ctrl+C" to copy the address)

With the Steam window open, click "Add a Game" in the bottom-left corner, then "Add a Non-Steam Game"

In the new "Add Non-Steam Game" window, click "Browse..." in the bottom-left corner, then go to the address copied in Step One. ("Ctrl+L" > "Ctrl+A" > "Ctrl+V" > "Enter")

Select COD.SCZ.Fov.Changer, "Open" , then in the "Add Non-Steam Game" window, click "Add Selected Programs"

You should now be able to launch FoV.Changer through Steam as a Non-Steam Game. Select the game you wish to play then launch the game using the GUI.

This method is more complex but is faster on a per-launch basis. Ideal if you do not intend to make changes between launches.

Navigate to the Steam installation game files in File Explorer. This is most easily done by Right-Clicking the game title in the Library sidebar, hovering over "Manage" , and clicking "Browse Local Files"

Alternatively, you can select the game in your library, open the Steam game settings (the gear icon to the far right) hovering over "Manage" , and clicking "Browse Local Files"

In a new File Explorer window (Ctrl+N), navigate to CoD.SCZ.Fov.Changer.exe. Copy the file, then in the Game files, paste the file.

Create a new text file within the Game files installation. (This can be done by right-clicking any empty space in File Explorer, hovering over "New" , then clicking "Text Document")

In the new text file, copy and paste the code:

NOTE: for the second line of code you need to replace the directory in quotes ("C:\SteamLibrary\steamapps\common\Call of Duty Modern Warfare 2") with your game installation directory. This is the same directory referenced in Step One, which you can select and copy with Ctrl+L)

NOTE 2: for the third line of code you may need to increase the /t option ("5") with a greater number. If you have a particularly slow load time (old HDD/CPU), or if the game is giving you a fatal error, try replacing it with 10 , You can also decrease or remove this line if you are confident in your machine and you do not consequently launch with a fatal error. Thanks to @Qdude for highlighting this issue in the comments.

Save the text file as "Run.bat" (You can do this with "Ctrl+Shift+S" , entering the name, then "Enter")

Open the game's properties in Steam and navigate to the General Tab on the sidebar (Rightclick in Library sidebar or Leftclick on gear icon, as per Step One, then click "Properties")

In the "Launch Options" box copy and paste the parameters:

You should now be able to launch FoV.Changer through Steam alongside the game.

Thank you for reading my guide. I hope it helps others enjoy an old game beloved by many more than just me.

If you have any difficulties, please feel free to comment and I will try my best to help you. I intend to add pictures and LinuxOS methods soon eventually. Any contributions would be greatly appreciated.