I liked the King and Toroko swap, that was pretty appropriate and pretty funny. I thought the Jack/Arthur swap was pretty funny. I was also amused by the way that Balrog and Misery didn't exactly swap roles, but seemingly swapped personalities.
I liked the creativity you had with certain changed lines. I was especially waiting to see what Kazuma was going to say instead of "those words on your cap," and chuckled pretty hard when he said "The words on your pants there..."
Some of the music changes confused me a bit. Is it on purpose that "Access" isn't playing at the beginning, when Sue is trying to contact Kazuma? And when it goes to Sue (originall Kazume) in that place the second time, is it on purpose that it plays "Gestation" instead of "Access"? I was taken by surprise when different music started playing in Egg Corridor, but I guess that one was probably on purpose and made a bit more sense.
While this was funny, this wasn't the most polished mod, there were several changes in lines that you forgot to make:
-At the beginning, when Sue is trying to contact Kazuma, you forgot to edit that text, it's just the original text of "Sue! It's me, Kazuma, your brother!" This confused me at first as to what your "algorithm" for swapping was. And then I realized that the entire script for that room was un-edited.
-One thing that was a bit off was that you start off by referring to the Doctor as a "she," but then in the next line, Toroko(?) says "If we don't turn Kazuma over, it might be you he takes instead."
-Also missed a pronoun change with King in the shack: "Toroko gets her ears all in a tangle when he sees Kazuma and I getting along."
Obviously, not everything is easy to do a "swap" with, but I thought it might have been a nice touch if you had swapped the Hermit Gunsmith with some other character, like Ma Pignon, or Chaba, or something else. Maybe you could have also done a swap of Mahin and Kanpachi. Also, since you kind of swapped around not just roles but in some cases appearances as well, it might have made sense to change Curly's appearance as well. Like maybe give Curly some of Quote's features, and vice versa. Just a thought.