They could just call it a refit and I'd be fine with it. Starfleet ships are modular - so goes the popular lore - so it shouldn’t be too difficult to swap out bits like nacelle pylons and engine pods and the ships neck and saucer and secondary hull. They did a whole stem to stern refit in 18 months so they could do the same to the ship in DSC. I just want it acknowledged so that I don’t have to make believe TOS and DSC are the same.
		
		
	 
Why isn't this bit from "Despite Yourself" (DSC) already enough?
LORCA: The Cooper!? Isn't she supposed to be undergoing a refit?
Why exactly do you think 
that was written in there, and filmed in closeup on Lorca loudly exclaiming it—and moreover, in what we now know with certainty to be 
mock confusion, no less—if not as a lampshade for what they were about to show us a short while later?
How hard do they need to hit us over the head with it? But as if that weren't enough to make their intent clear, Ted Sullivan 
confirmed it on Twitter. What they were doing there was quite deliberately 
re-establishing—in a manner I'm sure they 
thought would be quite sufficient for any of us who would understand the reference, or care remotely, little did they know—the 
in-universe basis on which a ship we'd previously seen depicted like 
this...
...might come to look like the above. Really, how much of a leap is it from there to the same rationale applying to the 
Enterprise? (Just as it did in TMP, which apparently we must have all forgotten and simply needed a subtle reminder of, right? Maybe I need a reminder myself, of where the heck in it anyone said that this was the 
first such refit the ship had during its lifetime?)
To your point about modularity and swapping out parts, that's apparently more or less 
precisely how John Eaves envisioned the DSC iteration gradually transforming into the TOS design, bit by bit:
"We had the advantage of a ten-year gap in Trek history to retro the ship a bit with elements that could be removed and replaced somewhere in the time frame of Discovery and the Original series..."
"...we split the struts so in time the cooling vent side could be removed to make it more like the Original TOS strut." 
(Here, it should be duly noted that the pylons themselves seem to have later been further altered from the initial version to which he was referring in those specific quotes—the first part transcribed 
here and the second part 
upthread by none other than @Tuskin38—but the 
principle remains much the same, just as you say. And 
according to @Ronald Held above, he has made further comments to this effect at the recent Las Vegas convention.)
If you're holding out for more explicit acknowledgement and explanation than 
that, I doubt that you'll get it. (Of course, I've been wrong 
before...I already owe someone a third of my precious bairns, but I guess two outta three ain't so bad!

)
	
		
	
	
		
		
			The whole fucking ship is completely different shape.
		
		
	 
You 
do realize this is 
exactly what people have said about the TMP refit for decades, right?
 
	
		
	
	
		
		
			It is much more different from TOS Enterprise than the refit was.
		
		
	 
Nah. Not really. They're all totally different from one another. The refit concept has 
always been a mere fig leaf used to provide in-universe cover for a desired visual update. Always, I tell you!
 
	
		
	
	
		
		
			The window is actually a thing that could easily be added or removed
		
		
	 
Good thing too, because it sure 
looks like one was indeed added at some point between "The Cage" and "Where No Man Has Gone Before" (TOS), and then later removed!
 
	
		
	
	
Oh, and were the nacelles and impulse engines changed too?
 
	
		
	
	
		
		
			Is the shuttle bay smaller now? I thought the whole ship was bigger (thus betterer) than before so the shuttle bay could be massive now?
		
		
	 
	
		
	
	
		
		
			It is much smaller if we assume that the versions of the ship are roughly the same size, which you obviously have to assume if you're going to pretend any sort of refit explanation for the changes.
		
		
	 
And just what size, pray tell, 
is the TOS 
Enterprise based on the shuttlebay? (And how much bigger does it get when one considers that the shuttlecraft mockup is both slightly smaller than its stated-in-dialogue size of 24 feet long, and 
also too small to contain the interior set we see for it?) I'll wait...
 
Or you could google it, like 
I did. (And no, that's 
not a LMGTFY link.

)
Now, then...
who's on first?

Enjoy your Friday night rebooty, everyone!
 
-MMoM