Vocalist TIP's and TRICKS from Lance King

well if your singing originals then new note choices are always your option,
if your singing a cover song or an original that many people have heard and know and love a certain way, it's best in my opinion to give them something similar (very close) if possible.

knowing the note, hearing it in your head before you go for it, is huge,
if you are having issues with this, and or just have anxiety about a note because it's at the top of your range, you just need to relax, and breath a nice relaxed breath just before you go for it and then nail the sucker!

Also depending on how hard your singing the rest of the set, you may need to ease back a bit on the other parts of songs and learn to pace your intensity and create more dynamics and not tire your voice so much.
 
Yeah, that statement was more for singing originals than covers, but even then, I'd say alternate notes aren't completely off the playbook, depending on the situation. If it's a song that the entire crowd is going to sing, too, and the melody is just THAT signature, then the vocalist better nail it. I'm thinking something like Journey's "Don't Stop Believing" as an example here.

We use that as a gauge with guitar solos, too. If the crowd can sing it, play the solo as it was recorded!