There are alternate harmonies written for last verses of hymns; in fact there are whole books of them. But they’re really only called last verses. I’ve been a chorister and cantor and friend of organists for 30 years and have never heard a special term for it. Now if the sopranos of the choir sing a special part above the melody, it’s called a descant, and that usually happens on the last verse. Perhaps that’s what you’re trying to think of.
Betsy