For the purpose of this tutorial I am going to use Call of Duty as an example and add a bind to the .XeX.

Firstly download xextool and a hex editor

-Now copy the .xex that you want to mod into the same folder as XexTool.

-Once you have copied it, open up notepad and type the following in

xextool -e u -c b -o default-binary.xex YourXexname.xex

-Replace "YourXex.xex" with the name of your xex, then save it as a .bat file in the same folder as XexTool.

-Run the .bat file and you should now have a 'default-binary.xex' in the folder.

-Open up the default-binary.xex in HxD and do a search for "exec viewSensitivity" without the quotes, you should now be able to see the following:

exec viewSensitivity_med....exec viewSensitivity_low....exec viewSensitivity_high

Click over to the Hex side and replace that all with 00's.
Before:
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After

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Then type your binds over the top of the 00's. For example, I will bind button back to noclip, jumpheight, field of view and unlimited ammo.

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-Alternatively you can type in "exec mods.cfg" and add all of your binds into a file with the name "mods.cfg", then put that file in the same folder as your game.

-Once you have added your binds or put in the exec command click save, then open up the .bat file you used before and replace everything with this

xextool -e e -c c -o YourXex.xex default-binary.xex

Replace "YourXex.xex" with the name that your .xex originally had.

-After it converts it back replace the .xex on your JTAG with the modded one and start it up, if you did everything correctly you should now have all the binds that you added

Credits too DavidxPxD