"Cheating" can have a legalistic meaning (broke the rules) and a moralistic meaning (did something you weren't supposed to to gain an "unfair" advantage). Examples of moralistic cheating which is not legally cheating abound: Luis Suárez in 2010 handling the Ghana shot off th line is a classic example. But whereas if you cheat in a legal sense you have to answer to whatever penalties there are in the system, when you cheat in a moralistic sense, you answer only to your own conscience (as I pointed out). Of course, in either case, you may face the opprobrium of those who observed you "cheat".
In this case, however, the "moralistic" side of the definition is questionable. What contrived measurable framework do you use to determine cheating on moralistic grounds?
If I save-reload because I'm playing a new game/version and I want to see what the outcome of a decision I'm unsure of using would be without having to potentially ruin my game, then okay. If I save-reload while I'm attempting an achievement and want to avoid unlucky consequences then, well, there's a reason most "ironman" modes attempt to restrict or discourage this idea.
Yes they do, but on what basis? Fundamentally, what has someone who got lucky due to reload actually accomplished beyond someone who attains an identical-in-every-way result with a simple reload? You're reloading in both instances, one earlier and more repetitive. You can of course draw this line further up or down the scale, and you also have the question of the moralistic framework in the first place. Generally, an "achievement" is something one earns. If one does not equate "time contribution" to "achieving", you're left with the choices a player makes in the game that influence the outcome. If you remove time investment, both approaches to, say, rolling a good replacement for Aztec's heir are identical in every respect. One takes longer, but in terms of skill and knowledge related to attain that good heir, the quality of play towards attaining it is identical. The problem is that this rationality is a slippery slope.
But I've played plenty of MP where one or more of the participants enjoyed exploring the boundaries of such behavior, and in my opinion, those games often got fairly contentious.
In MP, the big issue is that not all players are aware of the hidden, unstated rules and thus believe they're operating under different rules than other players believe. "Don't use exploits" is like a neon sign just waiting for some idiocy. Did that guy abuse missions for 100 AT, or was he just lucky? Is vassal/annexing Jolof as Brunei in 1490 and then finishing westernization by 1520 an exploit? Well, the rules said you can't deliberately sell provinces to westernize, but that's not what happened there, is it...so exploit or not for a Portuguese player to agree to allow this even if only temporarily?
Then people disagree, a GM makes a ruling, and that ruling is often a rules-made-up-as-you-go junk outcome...especially because vassaling a nation an then annexing is not exploitative in the vast majority of gamers' viewpoints, until you vassal the wrong nation, which wasn't ever explicitly stated in the rules, and isn't the only way to do it.