As far as Klingon Academy goes though, Chang is implied to have known that the Khitomer conspiracy was dishonorable, even "protecting" his protege by disassociating with him immediately beforehand.Chang, by contrast, is a Klingon war hero BEFORE his treason [see Klingon Academy] and died in an epic battle against Captain Kirk. He is a figure with panache and the sort of guy who fits in with the Klingon sense of superiority.
And it helps to remember Chang is a TOS Klingon not a TNG Klingon. Things like stealth, treachery, cunning, and intrigue are things they celebrate rather than condemn.
Torlek: General... Chang, I know that you blocked my nomination to be the next Military Adviser. So why this friendly farewell? We both know you still harbor a grudge for my actions at the Tal'Ihnor nebula.
Chang: [shaking his head] No. Time has made me realize that you were simply doing what I had taught you to do,
Torlek. You conducted yourself as a true warrior, and you did so superbly. I bear you no grudge. It would be best, however, if you left the Empire for some time. We stand at the brink of a difficult new future. This future will discard its old heroes and raise new ones. You are the finest student I have ever taught. You must claim your proper place in this future, while I must step aside. In the past, you served me as a loyal warrior, a friend, and my conscience when things were at their worst. But where I go now, you cannot follow... and I will need no conscience but my own. [looks grim for a moment, then looks up and smiles] Farewell, Torlek, son of Ro'vagh. [turns to walk away]
Torlek: "Conscience"? [Chang stops and turns back] What have you resigned yourself to, Chang?
Chang: Some rise by sin, and some by virtue fall.
Also Chang dying in an epic battle against Kirk probably doesn't do much to undo his previous dishonorable acts for the Klingons. We know Klingons like Koloth respected Kirk as a warrior and Chang only fought Kirk after dishonorably framing him for a crime and trying to get him assassinated on Rura Penthe instead of facing Kirk himself like an honorable warrior would. Yes, he faced down Kirk later but only after said plans had failed. Duras also died in an epic battle against Worf but Klingons were still speaking poorly of him afterwards because of all his dishonorable acts before his fatal duel with Worf.