Good lyrics should never be interchangeable. These are not camp songs. If you can be flippant about a lyric, it must not have been so rock solid to begin with, at least in your perception.
Look, I think Abie is untouchable as an English lyricist. But this is not Toras Moshe Misinai. You're coming off a tad strong. Skipping "he said" before saying "no simcha is a burden" is being flippant and not thinking a song's lyrics are rock solid? You know who would be laughing his tuchis off reading this (I'm guessing)? Abie. They're covering the song precisely because they think it is incredible. The subtle changes they and Kunstler make in the melody, lyrics, and arrangement make their cover unique.
This is a known phenomenon in the Jewish music world. MBD does not remember the lyrics to his own songs. I've heard this from more than one person.
He doesn't need to remember words to read them off a paper in studio recordings. FWIU, Happy Days was changed because of the way people were singing the original. "There were millions dying, in the camps of gas, while all the nations of the world just sat on their ...."