The most notorious change, and the first really horrible music change that WKRP suffered, was the end of an episode where Mr. Carlson's wife announces she's pregnant. (She was played by Allyn McLerie, from the musicals Where's Charley? and Calamity Jane; she'd played a regular role for many of the same production people on MTM's The Tony Randall Show, which Ken Levine wrote about recently.) The closing scene had them deciding, as sitcom couples always do, that they want the baby; to celebrate, Mr. Carlson asks Venus to play something "soft and sweet."
In the original broadcast, Venus plays "Thank Heaven For Little Girls" from Gigi. This is a joke that plays off several things that have been said or done earlier in the episode, which I won't describe here, but anyway it works perfectly for the scene.
In the mid-'80s, MTM suddenly redubbed this scene and replaced the song with "We've Only Just Begun" by the Carpenters. This kills all the jokes related to the "Little Girls" theme of the episode, as well as the joke of the extreme inappropriateness of playing this song on a modern pop/rock station. And of course Venus is holding the Gigi album at the end even though the song is no longer from Gigi. Kind of kills the episode, really.
I've never found out why this happened. Normally music changes occur because the original music is too expensive, but I doubt that that applies in this case. Someone has suggested that because "Thank Heaven" is (mistakenly) thought to be a song about pedophilia, someone at MTM might have decided to remove it for fear of getting complaints. I have no idea if this is true. When the commercial DVD comes out, of course, they'll probably just solve the problem by cutting the scene altogether.
All this detective work to track down the missing music -- there are some pieces of music and footage that may just be lost forever unless someone locates a copy of the original CBS broadcast -- may explain why some of us feel more strongly about WKRP than about many other good shows. No other show exists in so many different, incomplete versions; assembling a complete version is like going through different folios to assemble the Authoritative Text. You don't usually get that with TV.
Two other, less boring, notes:
1. Allyn McLerie, who was on Tony Randall and then WKRP, is an example of how production companies in '70s and early '80s often used to have a "stock company" of guest actors. MTM, Norman Lear, Paramount, Universal Television and other big content providers all had certain actors whom they particularly liked and would use whenever they got the chance, on different shows for different networks. In the '80s, this changed a bit; by then it seemed that the networks became more involved in the casting of guest parts, with the production companies having a bit less leeway over whom to use. (Brandon Tartikoff at NBC had certain people he would constantly re-use in guest spots on every show, no matter which company was technically producing it.)
2. For fellow cartoon obsessives, the way music was used on WKRP may seem quite similar to the way music was used in classic Warner Brothers and MGM cartoons. A lot of times, a song snippet is there because the title or theme of the song has some kind of connection to what the scene is about. So after the famous Turkey Drop, we originally heard about ten seconds of Creedence Clearwater Revival's "It Came Out of the Sky." It's what Carl Stalling would have done if he'd been using rock songs.