Vader never says “mother” so it had to be by name. I’m not sure how popular it is, but I’ve seen done before, and am personally in favor of it.
I recall someone mentioning that the James Earl Jones reading of the Bible is a place to find different varaiations of the word mother. You could find a phase that uses the word similarly to how Vader is forming his sentence and then see how well you could make it match through some audio manipulation.
Honestly still just too much work in my opinion for such a small change.