I would assume that "25%" was Eaves's supervisor's way of saying, "Make it different, and make the differences noticeable but not overwhelming. Make the
Enterprise fit into the DIS design aesthetic, but don't change it so much that it's not immediately recognizable
as the starship
Enterprise to most audience members." I wouldn't take it to be a literal quantification.
I always found the idea that CBS would be legally prohibited from using the Matt Jeffries design as a result of the CBS/Viacom split nonsensical. During the split, CBS retained ownership of all of the ST TV shows and of ST as an intellectual copyright; Viacom had to make its films under license from CBS. So the idea that CBS would own
Star Trek as their intellectual property, and would own TOS as their intellectual property, but wouldn't own an element
from TOS as their intellectual property, is... counter-intuitive.
Edited to add:
As for the Enterprise... perhaps she was launched in her Discovery configuration (let's call it Mark I design) and this is what she looked like during "The Cage". In the next seven years, she'll undergo a massive refit to Mark II design (WNMHGB & TOS & TAS), with a few changes here and there. Another massive overhaul will take place in 2271-2273, where we get the Movie era/"Enterprise class" design (Mark III). Two massive refits, retconning only The Cage, works better than other ideas that would involve some backtracking and as many as five refits.
That would work for me! Given how many elements of "The Cage" were subsequently retconned -- laser pistols being replaced by phasers in TOS proper and phase pistols in ENT; Taylor's reference to "breaking the time barrier" since the
Columbia crashed and references to "time warp factor X;" Spock behaving emotionally; the
Enterprise being referred to as an Earth ship rather than a Federation starship; Pike being uncomfortable with women on the bridge, as though women in leadership positions is a new thing in his society; Pike telling the Talosians he comes from "the other end of this galaxy" vs. later shows making trans-galactic travel something that takes decades; and the fact that the
Enterprise already had a different configuration in "The Cage" vs. TOS (taller bridge dome, larger deflector dish, spikes at the Bussard collectors, plates instead of round orbs at the back of the nacelles)... Yeah, I think so much of "The Cage" is already subject to later retcons that I'm okay with going with the DIS configuration as the 1701's launch configuration, with the TOS configuration as the result of a refit some time between 2258 and 2266.
My assumption, right now, given that Discovery Season 2 was all about returning to the status quo, and SNW seems to be all about "bringing back classic Star Trek" (literally even), they'll probably 'explain' the starship's appearance during the run of the series, with little changes here and there and perhaps a grand finale that will merge the ship with it's design from Enterprise's finale. The 'explanation' is not going to be pretty.
Oh, I dunno, I think it might be a fun element for the finale to feature the ship reaching its TOS configuration!