Well, I'm not sure if you call this a hack, but it's called a Game Save Hack. To make this work you will need a USB Mass Drive (Flash Drive) so you can save your game save data to your flash drive. You will also need Call of Duty 4 PS3.
Once you got your flash drive, plug it in your PS3 USB Port.
Go to the Game Section and go to Game Save Data Utility.
Find your Call of Duty 4 Game Save Data and Press Triangle and Press Copy.
Before going to your computer, get another copy because when doing this you have to start over Story Mode.
Okay, now since you have a copy of your gamesave data in your flash drive, safely remove the Flash Drive off of your PS3.
Plug it in your computer and open up the folder.
Open Grado_SP with Note Pad. By Right Clicking on it.
Paste this code:
put this in Grado_SP
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set breath_sprint "1"
set player_sprintSpeedScale "7"
set jump_height "99999"
set bg_fallDamageMaxHeight "99999"
set bg_fallDamageMinHeight "99999"
set cg_laserForceOn "1"
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After that, safely remove the flashdrive and plug it on your PS3 again go to Game Save Data and open up your flash drive and press triangle on the CoD4 Save Data and click on copy.
And then WALLA, it's done.
These codes will make you Jump Really High up in the Hair, have lazors on any gun, and make you sprint faster!
This will not work ONLINE!!!
Only Story Mode, it's just for fun.