Most games are designed to operate around a certain balance. This is generally normal mode. Easy weighs things in favor of a player while hard weighs things in favor of the cpu. Cheating via codes essentially weighs the scales several tons in favor of the player. A very very very very easy mode perhaps, but what separates this from just an easy mode is that it usually involves no way to lose and prevents game mechanics from working as they should.
A case might be made if the cheat involved is not invincibility but instead something less game breaking like extra funds. It could be the game might be very frugal with reward such that the person would be put off unless they had a little bit extra. This would probably not break the game as the capacity to lose is still there and would thus be akin to a very easy mode.
Again, it comes down to what the cheat will do, the desires of the player and developers, and various other factors. Anything that heavily skews things towards the player such that the cpu can almost never compensate would probably be cheating though; something beyond the favors granted by an easy mode that is specifically for people who don't want as much of a challenge or are new to the game.
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There is no shame in not knowing; the shame lies in not finding out