First, you have to run CH. Then, while X-COM is running, open up the game executable.
Load a save game, then SAVE that game again, in a fresh slot. Load that save game (you do not want to corrupt your good save game, trust me on this).
Once your in game, with the 'test' save game loaded, go into the Situation room, and click on the grey market. This is where a hell of a lot of patience comes into play especially if you only have say a unit of one or two available.
CH has an awesome tutorial, so I'm assuming you've already checked it out. If you don't understand it, you're more than likely over thinking it.
The cool thing about CH, is that say for example, you want to increase the number of UFO Power Source's. But you only have two. Now that you have CH loaded, and the game executable loaded within CH, you will put the number two in the value field. Run first scan, you'll get a huge list of possibles. Swap back to the game, and sell one unit. Swap back to CH, then run next scan with the new value. Your list just got a bit smaller!
Now, here's the awesome part, some of those hex values, starts to randomize when you go back in game and start to move around in base. In this case, I would leave the grey market and I just start to swapping around from from engineering to research to foundry (this is just an example, and action within base will work). If you go back to CH, and run next scan with the same value, your list will get that much shorter.
The challenging part is that you can't leave the current game and reload the same saved game, because the hex pointers are random (I'm sure there is a technical term for this). Now, if you are lucky and find the right hex, change the value to the desired number, verify it changes (and it does change once you move your mouse point over that unit) then you can save that game, exit to main menu and reload it to verify no corruption. If there is no corruption, viola! You've managed to edit a value!
The tougher edits are like engineers and scientists and finding the value to reduce panic in Council nations, etc!