Basil C. Thurston III

One of your favorite bands is coming to town, you pony up the bucks for tickets, get excited as the show day approaches, enter the venue with great expectations, applaud mightily as the band takes the stage, and then......they play some, not all, of the songs differently than as recorded- not just live variations, but full on tempo changes, rhythm fluctuations, lyrical changes, or, for me, the dreaded worst, a change in vocal technique that almost makes the song sound like a mockery of itself. It disappoints me even though I can understand an artists tiring of playing the same song the same way for 30 years- for me, if it's not better, stick with the original until you come up with the better version...watched an episode of Jools Holland yesterday on Palladia, and he had Steve Miller as a guest, he did Abracadabra, and he sang it so different, in an altered vocal style, that is was distracting to me, and made me disinterested in the performance.
Saw Steve Forbert play last week and he changed Romeo's Tune significantly, so much so that many around me had no idea he was playing it until he got to the chorus..
So when is it okay for an artist to change the hit song, to keep themselves interested, knowing that fans may not approve or appreciate it?