Yes, Ian, and has been discussed several times here, that includes key modulations, tempo/rhythm changes, etc. etc. ...

I LOVE to sing, and I wouldn't play a senior gig without doing it, but I have played gigs where only instrumentals were wanted, and I did not get bored ...
Funny thing, speaking of senior gigs, I was doing a routine at one and I did a 'Dick Contino' style version of "Lady of Spain" using the accordion voices and they LOVED it ... but that was only one instrumental mixed in with the vocals ...
But, that's why there is vanilla, chocolate, and Ben and Jerry's Cherry Garcia and New York Super Fudge Chunk !!!