Huge post incoming.
That it's not possible to tell which lines were written with Spock and McCoy in mind? That's false, of course, because it's easy to tell.
Only in some cases.
That it's not possible to deduce that some lines were written with Spock and McCoy in mind unless one is already aware that this happened? That's properly debatable. But it splits to two questions: are the characters so much out of character that the audience notices something amiss, and are the characters so much in each other's character that the audience can make the connection?
In my opinion, no to both, which is the crux of the thread.
Scotty is not Scotty in the movie. "Our" Scotty would tease Kirk, sure, but he wouldn't have "theories" - he would have answers. That's just this ONE line not properly rewritten, but it's enough to cast doubt on the character, and enough to make one decide that Scotty is being Spock if one has already been told that the writers originally intended it that way. ONE miserable line mangled by the rewriters. Apart from that one, it would have been more or less fine.
I've already acknowledged that this was a "Spock-ish" line, and I think your reasoning works: Scotty is more the answer guy, Spock is more the theory guy. So here I somewhat agree, even though I don't think that Soctty simply saying he has a theory is that out of character for him. If one hasn't been previously informed about the Spock-Scotty replacement, I'm not convinced they would notice.
Except, of course, for the fact that Scotty never volunteered to adjust the deflector, which goes against his general character (always the good soldier, always defending his captain) and plot logic (why would Kirk know anything about deflectors, and why wouldn't Scotty?), and is only excused by the fact that Scotty is also an acknowledged transporter wizard and might be further needed in that role. But that further need could have been better rewritten, too.
I admit, this is a bit of a hole in the movie: Kirk being the one to adjust the deflector is a contrivance just so he gets sucked into the Nexus, not because Scotty or even Harriman should have gone, but someone else entirely. Aren't there any Starfleet personnel hanging out somewhere other than the bridge, or are they not arriving until Tuesday as well?
So while I agree this is a problem, I
don't think it's a problem that has anything to do with the Spock/Scotty issue, because I DO think they did a decent job covering Scotty's reason for staying on the bridge. He was manning the ops console, and clearly had his hands full; to quickly pass what he was doing to another officer and expect them to pick up right where he left off would have been difficult, and when Kirk is in deflector control, we hear Scotty tell him "I dunno how long I can hold it together!"
Chekov is being wery much Chekov in terms of character. Nothing wrong with that. Not even when we get the one compromising scene, the one where he appoints nurses. That's how Chekov would do it - he always was one for abusing his formal authority and barking orders, while making everybody else feel the guilt for it. That's splendid Chekov, in fact.
I agree.
What sadly makes no sense is the idea that he would be appointing nurses. He's never shown any medical competence (despite accumulating more than his share of medical woes).
He's never
shown any medical competence, but doesn't it make sense that a seasoned Starfleet Commander would have at least some? Furthermore, who else would be a better choice for this
other than Chekov?
He wouldn't be appointing nurses. He would be putting together a medical team out of a disorderly and incompletely manned sickbay crew, appointing a preexisting nurse as Chief Surgeon
WHAT manned sickbay crew? WHAT preexisting nurse? There is
no medical staff. Not till Tuesday. Now, whether or not one thinks the whole "we are underequipped... till Tuesday" gag worked or not is another question. But in the movie as it was, he could not have done what you suggest.
and then shepherding in some reporters to serve as nurses.
Which is different from what he did how?
Or he would interrogate the reporters and VIPs in classic Chekov style until he managed to extract a confession that one of them had medical knowledge, then appoint that person as Chief Surgeon.
While I agree this would have been a hilariously awesome scene, it would also have been a much longer scene than was practical for the Ent-B sequence.
Not a question of rewriting the lines to better match the character here. That was all right for Scotty, and almost worked, save for that single line. Here, the character is fine. But the plot needs to be reworked around the fact that Chekov isn't a doctor, and the writers fail. Epically.
Again, I ask: who would have been better, among those present, to handle the medical situation? If you feel that the "no medical staff" bit should have been dropped entirely, I don't agree, but that's a perfectly valid viewpoint. But since they DID keep it in, who else would have been BETTER than Chekov to go draft some nurses and head down to sickbay?
So IMHO two failures, one on Scotty's character, one on Chekov's plotline. Both of them limited to a single line, a single event, in an otherwise flawless save - but both of them quite crippling if one already knows the characters were shuffled.
And I disagree that they were crippling, for reasons I've outlined. I'll even go so far as to say that it probably would have been better if they'd changed those things more, but I consider them very minor flaws, not crippling.
The audience will notice something amiss. It is perhaps not obligated to realize that Scotty is being Spock or that Chekov is being McCoy - but both the offenses, while very small and isolated as such, are highly characteristic of their specific characters, because only Spock has "theories" in Star Trek, and only McCoy is a doctor in Star Trek. Having theories or being an MD are not generic qualities in Star Trek. Those things should have been better rewritten.
I just don't see that. I don't see why the characters have to be confined in such tiny little boxes. I honestly think it's a huge stretch to say that the Scotty line was bad because "only Spock has 'theories' in Star Trek". This is really the mindset? No one else is "allowed" to use the word "theory?"

And:
I don't see how it is. The whole line is:
"There's just no way to disrupt a gravimetric field of this magnitude! (pause) But I do have a theory."
I can't imagine Spock talking like that. I'm sure it was rewritten for Scott. The technobabble that follows fits Spock more, but I can also imagine it being said by Scott, Obrien, or Geordi equally well. Spock's "speech pattern" has a lot to do with the way Leonard Nimoy delivers. Same with the other characters. There's nothing in that scene that fits only Spock.
This. The delivery doesn't sound like Spock at all, it's very frantic and stressed, the way Scotty tends to talk when the crap is hitting the fan. Also, saying essentially "This is impossible", yet then immediately saying "But we're going to do it anyway", seems VERY Scotty to me.
And for only McCoy being the doctor... Chekov wasn't trying to "be the doctor", he was taking charge in a situation in which there WERE no qualified medical personnel present, period. Should the creators just NEVER be allowed to construct plotlines that force characters to act outside their specialty? Situations where trained, specialized personnel aren't available DO come up.
So, yes, the deleted scenes
do count, in the sense that they indicate the creative decision-making that went into changing the "Big Three" into the "Slightly Lesser Three."
For this thread, no, deleted scenes have no relevance. The point of the thread is to discuss the
finished film. A line from a deleted scene has no bearing on lines in the movie, except to help establish the fact that - behind the scenes - the scenes WERE rewritten from Spock and McCoy to Scotty and Chekov. But, as I also said in my OP, I'm already aware (as I think everyone here is) that that is what happened. What I'm trying to focus on with this thread is how the lines
play on screen. Which specific lines sound like they weren't changed enough from Spock/McCoy to Scotty/Chekov, and why.
I think the most obvious Spock line is "Captain, is there something wrong with your chair?".
That's a Spock line to you? Specifically?

Maybe this is just too subjective a topic... How on Earth is that a Spock line? It's not an "anybody" line; it doesn't sound like anyone in particular to me. Only the delivery makes it distinct, and I think Doohan nails it.
And as I mentioned in my OP, there are
several lines that sound to me like they WERE tailored for Scotty and Chekov.