[djur]

Unfortunately, that joke on DS9 (which I absolutely love) was taken as establishing as canon that TOS-era Klingons actually looked different. A sane person would interpret it as a meta joke in an episode full of them, but these are Star Trek fans we're talking about here.

That still doesn't justify Enterprise trying to explain it. If one must insist that there be an in-universe explanation because of the DS9 precedent, just say Q decided to mutate the entire species for a hundred years as a lark.

[jonnathanson]

The classic "a wizard did it" defense. :) Come to think of it, that's just about the only potential appearance of Q in Enterprise I would have tolerated. "Oh, they look different? Hmmm. Q did it."

[Pxtl]

My favored approach would be to just do it off-camera.

One episode right at the end, Klingons show up looking de-Klingon'd. "What the hell happened to the Klingons?" Klingons won't say.

Sometimes, the audience just doesn't get to know.