On the other hand, judging by the answers of the most brilliant writer of the whole country of delirium, she could change her eyes by inserting lenses. And the answer would be— because she wanted to. And let the reader fuck with the perception of this character, yes.
I really hope changing characters eye color using contacts isn't going to be a common or a future practice that is not extremely temporary or just for the short lolls. It's because there are instances where eye colors are used as a part of the storytelling, Nao's heterochromia origin, Kaori's sudden shift into red eyes, etc. To me changing eye colors without a good plot reason voids the importance of those segments.
Btw for some reason I accept new Rin much quicker than new Chika. They're all lovely, yes; while I can trick my brain into registering the new Rin as like a shiny version of her, I can't help but seeing Kirin in this new Chika; their designs in my eyes now overlap too much.
Never heard of the real-life post break-up makeover? I know the context is different but it's not unknown for people to radically change their entire look pretty much overnight.
Because the efforts in molding an old Chika into a new Chika to me are enough to mold Kirin into this new Chika or, on an extreme end, mold Maya into Otoha. At that point calling these new models actual new characters will not feel incoherent; the change is that substantial.
We (or at least I) need these changeable facial features to stay roughly constant to properly recognize them as different individuals, especially when all them girls are generated from the same koikatsu model; literally 20 clones with close to identical facial structures. Change their features with or without plot reasons, sure; it doesn't mean it won't be confusing in medium like renpy.
Btw if you watch One Piece, it's an epitome of changing hair/eye color = making a new character
. It's even more indistinguishable for manga readers from time to time.