We used to do a French song that can only be described as sexist and ageist. We would introduce it by saying something like "the sentiments expressed in some of our songs don't reflect the opinions of the band" and make a joke of it.

I take songs on a case by case basis. I don't clean them up at all. If I decide to do a non-PC song, I just say I'm going to do a non-PC song, it's from the 18th or 19th century, this is how people felt back then, and isn't it nice that we've moved on? That said, I'm not drawn to songs that have overtly racist lyrics. If I really like the melody, I can always find a different set of lyrics to go with it.