And really, they HAD to change the Klingons a little bit, and make them more honorable, because if they were all dishonorable, bloodthirsty betrayers like TOS Kor, wouldn't it violate the Federations' basic principles to ally themselves with the Klingons? I mean the very term Empire in Klingon Empire indicates that the Klingons take over world by force. So they had to tone down their villainy somehow, hence the code of honor concept.
See, the trouble for me really begins because it does lack consistency with the Klingons in TOS. Oh sure, the excuse could be made that the Klingons in "Errand of Mercy" had their own
interpretation of ethics and honor to which they were subscribers, or that as military
officers fighting against the Federation in a state of near war, they put aside those rules of conduct (or 'interpreted' them very loosely). But on the other hand, there's little indication that TOS Klingons care for honor at all.
I suppose (retconning like a man possessed) we might say that for the TOS Klingons, the scent of blood and the glory of battle temporarily supplanted their need to be honorable opponents?