Verican: Yes the insane difficulty saves will be marked dead, but you can still load a game that is only hard difficulty, as in, I am about to fight a boss on insane mode, I change to hard and save my game, go back to insane to attempt boss and die, I can now load my game on hard mode, return to insane difficulty, and try again.
Seems you're right and I was wrong to repeat what someone else said. That basically ALL your savegames would be marked dead if you try to load a save out of insane mode and have ever died in that game. There was also this one guy whose saves were all marked dead, after he died in a different run after completing one on insane. Seems they didn't find a perfect solution for this insane business.
But it would still not be right to diminish the game for all players that don't want to play insane, but perhaps adjust the difficulty later in the game.
The demand for difficulty change in the game was there in the first Witcher, that's why Flash made a mod, which remedied the lack of the feature. And RED, who listened to their fans, thought it might be a good idea to implement the feature in the new game.
Anyway, if you cheat your insane play with the trick you mentioned, who are you actually cheating? Only yourself. Allegedly, the enemies in insane are harder than in hard, so that might be a reason to want to play that difficulty. BUT maybe you dont want to die at a point in the game that tends to be glitchy and thus lose the complete game. I'd be good with "cheating myself" at such a point. It's not like I need to compete against myself. ;)
Oh, that leads me to another question (since the first assumptiuon was wrong): can I load up a game in hard where I died in insane?