There are no ini tweaks, hook injections, hex editing, or native methods to directly modify the FOV value.

This is a driver-level solution I've come up with that sacrifices vertical resolution for wider peripheral vision. This trade off between wider vision and full frame resolution may not appeal to everyone.

This FOV workaround also works great in windowed mode. If you are interested in playing windowed, please read my other guide.
 

These reference screenshots should help you understand the difference in horizontal peripheral gained, starting from narrowest to widest.

As you saw earlier, the increase to the FOV in 64:27 (aka "21:9") ultra-widescreen is a considerable leap from 16:9 standard widescreen. So for this guide, I will be using that aspect ratio because it gives enough of a boost to the peripheral vision without losing too much vertical resolution.

You are free to substitute with a wider aspect ratio of your choosing. Whatever you wish to use, we must first convert the aspect ratio into a decimal number:


Now divide your game's width resolution by the aspect ratio decimal number you just calculated. The result will be your new height resolution:


So if you normally play this game at 1920×1080, your new resolution will become 1920×810.

After figuring out what your new resolution is, you need to add it to your GPU driver so the game can recognize in the video options.

For this guide, I will be working with the Nvidia Control Panel. However, the concept of adding a custom resolution remains the same with AMD driver software.

1. Right click on your desktop, click NVIDIA Control Panel
   
2. Expand Display, then click Change resolution
   
3. Click Customize...
   
4. Click Create Custom Resolution...
   
5. Enter your new width and height into the Horizontal pixels and Vertical lines fields
   
6. Click Test then confirm the test

If everything went well, your custom resolution should show up in-game at the end of the list.

You will be using a program called Widescreen Fixer that will allow you to use a custom aspect ratio in Rainbow Six Vegas 2, which will simultaneously scale the FOV and HUD accordingly.

On Widescreen Fixer's homepage[github.com], download the latest version.

Extract the archive and run Widescreen Fixer.exe.

Under Select Game, choose Rainbow Six: Vegas 2 from the dropdown list.

Click on the big gear icon to the right, and make the following changes:

1. Uncheck Automatically Detect Aspect-Ratio
   
2. Choose Custom from the dropdown list
   
3. Enter your new width and height into the Custom Aspect-Ratio fields
   
4. Click Save Settings then Close Window

You can enter your custom aspect ratio (64 and 27) instead if you prefer, but it's much more fool proof to just enter your resolution (1920 and 810.)

Leave Widescreen Fixer running in the background and start the game.

You must be in a mission for Widescreen Fixer to work correctly. The quickest way is to start a single player Terrorist Hunt. Once you have spawned, press the multiply key (*) to enable it. Now you can quit the mission and the fix will be applied to the menus as well.

The multiply hotkey can be changed in Widescreen Fixer under the Settings tab.

Some graphics such as black borders from night vision and thermal vision don't extend to fit your custom aspect ratio.