That's a pretty cool idea. I'm sure the Trek "expanded universe" is full of abandoned-but-neat ideas!
I don't know the details and too lazy to seek it out, but I'm fairly sure there is a canon or semi-canon explanation that explains the changes as some sort of genetic virus that swept through Klingon worlds during TOS era changing Klingons to look more human.
Really, it's all too much work!
I like how they treated it in the DS9 episode when our heroes go back in time to Kirk's Enterprise and encounter all sorts of anachronisms, including Klingons who look very different from Worf! His response? "We don't talk about it."
Lately I've been a bit fascinated by the Trek "expanded universe" of novels and comics. Since none of these are ever considered canon, they often match up with canon when they are first published, but then become out-of-date as TV and movie Trek continues to expand. Newer novels/comics then ignore the elements of older books/comics, only themselves becoming out-of-sync with canon over time. So, if you went and read the thousands of Trek novels and comics that have been published over the decades they would not only be wildly inconsistent with canon, but even with each other! Nothing wrong with that, just interesting!