Start up your PS3 and insert an USB stick in your PS3. Now go to 'Saved Data Utility' (under Game). Select your CoD4 savegame and press triangle. Now do copy and select as destination your USB stick.

Put your USB stick in your computer. Click on the map 'PS3' then the map 'SAVEDATA' then 'BLES00148-AUTO-'. Now you see the GPADO_MP, GPADO_CM and GPADO_Sp files. Open them with noteblock (or how it is called) or another program and start to edit them (bunch of edit tips on this site believe me).
Now when you made everything like you wanted it save it on the USB stick. Put the USB stick in your PS3 and go again to 'Saved Data Utility'. Now press x on 'USB Device' and you will see some data on there. Press triangle on the CoD4 data to copy it from to USB to the PS3.

Now in order for the hacks to work you need to delete the patch (which will block your hacks from working if you haven't deleted it). The patch is located in the 'Game Data Utility' under Game. Just delete it (the CoD4 one, patch 1.40).

If this answer wasn't what you asked for then sorry =P. I was just trying to help. Note that if you make hacks in the GPADO_SP file you won't have to delete the patch (as you are making hacks for singeplayer). The GPADO_MP file is for multiplayer (splitscreen) but can be used to edit online gameplay too. The GPADO_CM file is for online gameplay but can be used to edit multiplayer (splitscreen) gameplay too. Gl

If you haven't seen it/read this thread: You must login or register to view this content.

It's VERY helpful.