In Stephen Schwartz’s musical “Children of Eden” there is a song near the end of the second act called “The Hardest Part of Love”. This lovely song is built around an acoustic guitar playing “rhythmic lead”, with pedal tones at the top over a moving bass line. However, the score puts the song in the key of Gb, which makes this approach difficult if not impossible…
My first strategy was to put a capo on the 2nd fret and play the song effectively in the key of E. This sort of worked, but didn’t quite feel right, and got more difficult in the latter part of the verse. Really, the song wanted to be played in G; my guess is that it was originally written in G, but somewhere along the line was transposed down a semitone to better fit the performer’s vocal range in one of the early professional productions. But you can’t use a capo to DROP the guitar by a semitone…
You COULD bring a separate acoustic pre-tuned down, or if you only had one acoustic, you could play it tuned down but with a capo on the first fret for the rest of the show…
Because I was already doing the show on my Line 6 Variax 300, my solution was to use the Workbench software to set up a custom patch based on the Gibson jumbo acoustic but tuned down by a semitone.
There is another song in the score (I forget which one) which is in F# and could be played with a conventional capo on the 2nd fret. As I’d already built the patch for the previous song, I used this to tune everything up by a tone.
The Guitar in Musical Theatre 
Interesting… The variax is clearly a very useful piece of kit for precisely these situations… But do you find a good guitar to play? Is the action good enough etc?
Personally, I’d love to get all the technology from a variax and transplant it into my Ibanez!
It’s nearly perfect for this sort of gig; there are only a couple of shows I’ve done where it wouldn’t be really useful.
The guitar itself isn’t that great – I bought the cheaper 300 model, but there is a very nice 900 model if you have a bit more to spend.
It is possible to attach custom necks (eg, by Warmoth) to a Variax, or to transplant the bridge/electronics into another guitar. There are luthiers near me who do this sort of thing, but so far I’ve not quite had the courage to put my Yamaha tele-style under the knife…