Back in the day (this would be the 80s and 90s, I'm guessing the turning point was the 9/11 "inappropriate radio lyric" freakout and the Superb Owl "wardrobe malfunction"), the classic rock stations (96 Rock and Z93) wouldn't censor anything. Either they played it as is or they didn't play it at all.
What has stayed the same:
Blasphemies:
G.D. in the Eagles' "Life In The Fast Lane" and "Christ" in Queen's "Bicycle Race" still get played as is, as they did then. I'm guessing if the FCC complained, someone could invoke the Establishment clause.
What has changed:
The first 4 of George Carlin's 7 Dirty Words:
--You used to hear the S-word; the most notable example being "Money" by Pink Floyd. Z-93 (the pop station) would censor it; Z93 (the classic rock station) and 96 Rock would leave it alone. Now they (River and Rock 100.5) censor it, and sometimes even the "bull" too. The same goes for "Jet Airliner" by Steve Miller; while pop would always play the "funky kicks" version, AOR would sometimes play the "funky s---" version, usually preceded by "Threshold". Not anymore.
--They would also play the F-word in The Who's "Who Are You". There was a single edit of the song that went "who the hell are you"; now you hear some totally new version that repeats another line of the song instead of going "who the (whatever) are you". Similarly, 96 Rock would occasionally play the uncensored version of Pink Floyd's "Not Now John".
--I've never heard the C-word on the air.
--The P-word is regularly bandied about by airstaff today. Not back then. Same goes for the milder crude slang terms for body parts. Nobody would dare play, say, Sammy Hagar's "D--- In The Dirt" back then.
Sex Acts:
--Rock stations used to play the verse about "giving head" in Lou Reed's "Walk On The Wild Side". Rock 100.5 sometimes does, sometimes not; River never does.
Ethnic Slurs:
--The Mother's Finest song "N------ Can't Play Rock & Roll" was controversial enough to not play back then. You won't ever hear it now.
Gay Slurs:
--The verse with the gay slur in the Dire Straits song "Money For Nothing" was customarily omitted in the single version played on pop stations. AOR stations played the whole song. Now River won't play the long version with the problem verse; Rock 100.5 sometimes does, sometimes not. The long version with the slur is becoming more common now.
--Related to that, when an old AT40 episode is playing the Charlie Daniels song "Uneasy Rider", a clunky period bleep censors out "asses", while a modern discreet mute censors the F-word. AOR stations used to leave both words uncensored; now they usually mute out the F-word and leave "asses" alone. Times change.
--Classic rock stations would play "I'd Love To Change The World" by Ten Years After uncensored; I haven't heard the song aired in a long time, but I guess they would mute out the "d---s and fairies" line.