I don't consider single player changes cheating. For something to be cheating, you need to break the rules agreed to by the players. If you're the only player, you presumably can't break the agreement you make with yourself.

I would further argue that it's a bad behaviour only if one cheats in competitive multiplayer games.

Almost a decade ago, I was having fun playing Left 4 Dead 2. There is this survival mode where you and your human teammates play against neverending waves of zombies. In one stage, there was someone who invented a way to defend yourselves on a bridge by all four players strictly crouching and shooting straight to the front, at the far end of the bridge. If anyone runs out of ammo, they walk a few steps to pick up a new M4 and come right back. Cooperation is the key in surviving for more than 15 minutes, and everyone must strictly obey this play style.

Anyway, the way to communicate between players were limited. It was hard to tell everyone what to do by typing. I downloaded a mod which grants us infinite ammo, that way, nobody needed to get up to get a new gun. In late game, there were three Tanks spawning and charging at us, that even with perfect timing it was hard to defeat all three. The infinite ammo absolutely helped, and I think I just created an new way of playing this stage which depends more on one's knowledge than skill.

I ended up had a great time with those strangers who played with me, who unlocked the gold medal of that stage, and way beyond the survival time requirement.