Comment by banana_giraffe

Not quite. The Game Genie presented a UI before the game started where you could enter codes. These codes were basically patches to the game's ROM. When the game ran, the Game Genie would intercept the requests for the bytes of ROM based off your code and replace them with a different value.

There was a prototype of a more advanced model that would be closer to what you're describing, but it never made it to market.