Codemasters tried to build a walled garden around Game Genie codes so they could sell you updated codebooks. The codes were hashed so they had little relation to the memory location they referred to.

What you really wanted was an Action Replay.

The Nintendo 64 Game Shark actually did. You'd set up filters for various conditions (e.g. RAM value is X, where X is number of lives, items, character position, etc) and ask the Game Shark to filter RAM addresses that meet them. Change your game state and re-filter until you're down to very few, then you could tweak the values to see if it changes what you wanted. Pretty neat, especially since you could do it right on the console in realtime.