I have very little patience for last minute changes, if I am volunteering my time. I have dealt with it by telling the worship leader, "I am sorry, but with my current schedule, I don't have the time to learn the new songs. You'll need to find someone else to play that service." Usually stops the inconsiderate behavior in it's tracks. And it rarely happens again.
On paid gigs, it's a different story--I do whatever I am able to make the client happy, unless their behavior gets to the point that it isn't worth the money.
On paid gigs, it's a different story--I do whatever I am able to make the client happy, unless their behavior gets to the point that it isn't worth the money.