Both of Ursula's reprises in The Little Mermaid "Poor Unfortunate Souls (Reprise) and "I want the Good Times Back (reprise)" were both used for set and/or costume changes
I know the long "we LOVEEEEEEEEE you" from COMPANY is as long as it is due to the elevator that was on the set, as it took awhile to move down.
"Oh look at the time, three more intelligent plays just closed and THE ADDAMS FAMILY made another million dollars" -Jackie Hoffman, Broadway.com Audience Awards
I thought Tomorrow was written earlier in the process, It's on one of the early bonus demos on the original soundtrack.
I forgot the "added during tech" part of the OP's question. I didn't mean to imply that "Tomorrow" was added that late to the show, only that Strouse says they only wrote it to cover a set change. That could have happened early in the planning process because they knew a set change would occur there.
Isn't Western People Funny in King and I there to serve an "in one": scene while the set is changed? I always assumed that's one reason it's usually dropped now (aside from the fact that it's not exactly a highlight).
I think the melody of "Something Was Missing" was originally heard as "You Rat You" in the film THE NIGHT THEY RAIDED MINSKY'S. Another scene-change utility (and one of my favorites) is "Her Is", from THE PAJAMA GAME.
"Brush Up Your Shakespeare" from Kiss Me, Kate was added at the end of Act II to cover a massive set change for the show's finale. It's always done in front of the curtain, and it's not really a part of any scene.
When I played the Mad Hatter in my community theater's production of ALICE IN WONDERLAND, The White Rabbit had an extra song that our director wrote to allow time for Big Alice to put the house on for the scene when she grows into the house. It was a song about if he were in a parallel dimension and was always way too early instead of late. Keep in mind, that was not an official song obviously, the director wrote it.
They all call me a troll. Ok, call me a troll. If I stand on my own, so be it.
"I've Grown Accustomed To Her Face", important as it is, is done "in one" to facilitate the scene change between Mrs. Higgins' home and Higgins' study (the same Wimpole Street drop used for "On The Street Where You Live").
Also, I believe, in the BRING IT ON tour, there was a scene when the head cheerleader and her boyfriend (I saw the show months ago, so I can't remember their names) had a sweet sentimental moment infront of the curtain. This was so they could set up for the big Cheerleading Competetion behind the curtain.
They all call me a troll. Ok, call me a troll. If I stand on my own, so be it.
Probably the most famous example is the title song in CABARET, at least in the original staging. The second half of the song is moved downstage to facilitate the scene change from the Kit Kat Klub back to Cliff's room, but moving Sally down to the "limbo area" and having her more or less "lose" herself in the number certainly ups the ante theatrically and emotionally for both herself and the audience. Good theatre.
Though it wasn't written for the express purpose, it was planned pretty much from the start for "I Just Can't Wait to be King" to be done as an in-one number to cover the scene change into the elephant grave yard.