Changing the key for a singer is a must. No professional would ever think about singing a song that was "out" of their range.
First question would be WHY?
Second question would be who wants to sound bad, like they can't sing and their voice is cracking?
If it takes the whole song until they finally find the right key, i do it. Then if they want to sing the song in its entirety, i'll play it again.
Showing people that you care and want them and everyone to sound their best, is why people love to come to your karaoke.
If i know the singer and know a song is out of their range I'll tell them that it needs to be lowered, before i start it.
If i don't know the singer, i will ask them if they have ever done this song before. And i tell them why. Some times they want it unchanged, sometimes they want it lowered and thank me for it.
The better i can make everyone sound the more enjoyable it will be for them, me and everyone listening.
I hate to hear someone struggling to sing a song that is totally out of their reach. For what good reason?
Some people think they "have" to sing it as it was written.
Where did anyone ever come up with that idea. "Can't be a man if he doesn't smoke the same cigarettes as me..." "And has to sing the song in its original key..."
Yeah sound like a jerk and rip up your vocal chords to be a man. It's why we are all here. Ohhh you macho thing you...
Hurt our ears some more. 