Culber said something right before he was murdered about how if there was another personality imprinted on top of Ash, they would have detected it. It slipped past them because "Ash" was written on top of Voq, rather than the other way around.
Culver said you can’t hide a personality under an existing ing one without it showing, but you can theoretically do it the other way round....
Yeah, but c'mon, that's just a couple of lines of dialogue written as an after-the-fact rationalization. It's not as if it has any basis in actual science, or for that matter in Trek lore, or that it even makes any particular logical sense.
They could just as easily have written this plotline without all the gruesome surgical aspects, and said that they implanted Voq's consciousness inside Tyler's brain as a "sleeper" personality, waiting to be triggered, buried so deep that it would elude standard Starfleet medical scans. Had they explained
that in dialogue after the fact it would have made just as much sense... actually, a lot more sense.
So you rebuild Voq to be more or less human...
And that's the part that really strains credulity. What's worse, it strains it all the more precisely
because of the (IMHO pointless) way they've redesigned the Klingons for this series. In the days of "The Trouble with Tribbles," given how Klingons looked then, it was perfectly plausible for Arne Darvin to be a Klingon spy with only minor cosmetic alternations to make him look human. Even with TNG-era Klingons, surgery to look human might've seemed plausible enough (although the bits added to canon about redundant organs and such would've made fooling the scans a bit of a stretch)... and once the Augment Virus was in canon, there was a ready-made plot device to make it even easier. But with
these Klingons? The notion of altering one to pass as human requires a really superhuman level of suspension of disbelief.
