No. The playlist and the uploaded show mp3 are entirely separate. I know this because I've had to do what I'm describing before. A song was out of place on a show, but the playlist didn't reflect this mistake because it's separate from the show mp3.

I can't guarantee that the playlist won't get erased; it just won't be altered. Don't take any chances, though. When you do this, edit the existing show rather than use the 'add new show' function. This should preserve the playlist. It does for me. I learned this trick the hard way. If the playlist is missing when you get to it, back out of it and whatever you do, don't hit save.

Just make damn sure to check that 'overwrite' box on the upload screen or things really will go sideways.