Know your audience.

No one except the most deeply neurotic of the deep South should be offended by many Yankee songs, because by general consent they're now considered "American."

But know your audience.

Minstrel songs sung in minstrel dialect are out of bounds for reasons of taste (call it "PC" if you wish). African Americans and many others find it weird and creepy, and maybe scary and insulting for white people to sing even "Jimmy Crack Corn" in minstrel or even "Black English" dialect. Normal English will work for songs without a racial component.

"Dixie" by common consent is kind of off limits, though you might get away with the melody alone. The "Battle Hymn of the Republic" is probably too pompous, pretentious, and apocalyptic to be sung for fun. (Check out *those* lyrics! Lucky that few people took that stuff 100% seriously.)

The sentimental stuff (like "Lorena" and "Aura Leigh" and "The Vacant Chair") is nonpartisan and always acceptable.

"The War of Northern Aggression" is a consciously tendentious name. Southerners supposedly prefer "War between the States" to "Civil War," but I don't know that anybody's ever monitored their actual usage, and frankly I haven't it heard it in conversation nearly as often as I've read it in books.

"I'm a Good old Rebel" was written as satire, but many will take it at face value unless you explain what's up with it.

Any non-minstrel song without any obvious politics in it is fine.

Never sing the "n-word" or the corresponding "d-word," unless it's clearly understood to be part of an educational, historical performance, preferably on a college campus.

Just speaking from my experience. Carry on.