I am aware that ENT retcons the change in Klingon physiology as augments Klingons. Is there an accepted theory as to why legacy characters who return after TOS, are shown to have changes? Do people simply retroactively apply the events of “The Augments”?
The difference between the klingons in TOS and the TOS motion pictures, was that klingons always looked like that, and in DS9, according to Worf, it was due to some unspecified thing that is not discussed with non-Klingons.
But other than that, not really. The official position likely has not changed.
In fandom, it varies. Some people treat it as a cosmetic choice, and that Klingons underwent changes as necessary, and others might stick to the one interpretation of what klingons look like for all of them.
Personally, I’m of the Diaspora opinion, where the varieties of Klingon all coexist, where some of the changes are racial, like they are in humans, and others not.
For example, T’Kuvma house were Klingon supremacists, so it seems likely that some of their more exaggerated features were due to genetic modification on their part to try and enhance their Klingon attributes and remain Klingon.
But B’Elanna? She’s just like that.