Beat the game first, but after that you should feel free to go crazy! You can get a ton of replay value out of enabling weird cheats, breaking intended progression, or experiencing the game differently when you're invincible or overpowered.
However, if you plan to use cheats merely to avoid a challenge in the first place, I would have to say a hard no on that. To me, that's antithetical to the medium itself. There are certainly games that aren't about challenging yourself, but the vast majority rightly demand some amount of skill and without that it's essentially empty. I personally abhor the idea that making games a cakewalk is 'progress'. Most games include an easy mode these days, and that makes sense for people with a low skill level since presumably it's still challenging for them. That should be more than enough.
Of course, some games have what we might call 'unfair difficulty', in which case it becomes more ambiguous. However, I would say that if you aren't happy with a particularly punishing game, just don't play it. Unless it's an arcade classic with unimaginative, bullshit difficulty that is meant to get more quarters out of you, game progress is not owed to you simply for owning the game.
