I'm sorry, but no. Don't do this because of that reason. I've read that scene multiple times, and it never came off as racist in any way, shape or form whatsoever - plenty of babies tend to bite the nipple while being breastfed, this isn't anything specific to any race, and is probably racist to try and paint it as such.
Have you people never heard of a woman complain about sore nipples from breastfeeding, or are we just going to sanitize anything and everything? This is exactly the opposite of hateful racism, but racism nonetheless...
I don't think he was talking about racism in this particular scene, but rather a form of sexualization of Luigi's act (biting the nipple).
The sentence: "Ouch, since his first teeth came out, he really loves biting my nipple between sips." gives the impression that Luigi does it voluntarily and he takes pleasure in doing it.
Coupled with this extra sentence : "He probably takes after his father. He loved doing that too." suggests that Luigi is doing the biting for the same reasons as his father.
The change would be very minor, based more on the choice of words used in these sentences than a complete change to the dialogue.
So "Ouch, since his first teeth came out, he really loves biting my nipple between sips." would become "Ouch, since his first teeth came out, he started biting my nipple randomly between sips."
And after "He probably takes after his father. He loved doing that too." I'll add a new sentence from Helena "Sarah ! He's just a baby, he doesn't know what he's doing and it happens more often than most people think ! It's certainly not for the same reason as his father..."
I think that would be enough, without changing the whole idea of the scene.
Give it a go, and forgive the visuals - the NTR/NTS story is absolutely fantastic. And as for the supposed flaw in my argument - I was trying to explain that the interracial aspect made the scenes even hotter, and that it contained no negative racial connotations whatsoever, as the growing intimacy between MC's girlfriend and the black guy in Pineapple Express is completely natural. That is why I said the skin color didn't matter, but because he was black, the interracial aspect gave that extra spice. To give you an example of an interracial romance done right, so you aren't so hesitant to write an interracial romance for Sarah.
I'll see... Since the start of the game's development, I've hardly touched another game, it's quite time-consuming...