Hey, It's That Guy!: Ko-Ko has been prone to the occasional stunt casting - including the likes of Eric Idle and Groucho Marx.
Political Correctness Gone Mad: The 1907 revival was cancelled for six weeks due to a state visit by Prince Fushimi Sadanaru. It backfired spectacularly when the prince expressed a desire to see the show. It backfired even worse when a command performance was put together and both the prince and his entourage found it Actually Pretty Funny.
Throw It In: When Yum-Yum reassures Nanki-Poo that she does not love Ko-Ko, his reply as originally written was simply "Rapture!" In an rehearsal Durward Lely, the actor playing Nanki-Poo, delivered the word "Rapture!" too strongly for Gilbert's liking, prompting Gilbert to tell him, "Modified rapture" (meaning "tone it down a bit"). Lely responded, "Modified rapture!" and Gilbert liked it and added "modified" to the script.