My guess is that when he was the understudy, he sang the songs in the original key and then they changed them when he took over the role full time. I would imagine that the current understudies sing it in whichever key is best for them, and the conductor tells the orchestra which versions of the songs to have up before each performance. It would be unusual to have new sets of orchestrations made just for the understudy; but if multiple versions already exist, it makes sense to use whichever key works best for each person (remember that every role has at least two people covering.)
When Faith Prince took over in "Little Mermaid", the keys for her songs were lowered quite a bit. Heidi Blickenstaff remained the understudy, and when she went on, still did the songs in the keys she always had.
It is a lot easier than it used to be to create transposed orchestrations, but there is still a bit of labor and cost involved. A new set of parts needs to be printed and bound and distributed, and changing the key can affect things like the synthesizer programming where you often have split patches and the left hand plays one sound while the right hand plays another. Changing the key may mean that a note that used to be on the RH oboe sound is now on the LH cymbal sound, for instance.
Updated On: 9/29/15 at 12:15 PM