I just saw this on the DK-TUG mail list. I seam to be the tool I’ve been wanting for years but been to slack to find. “Slack” since i couldn’t imagine that such tool should not exist. It’s ‘iconv‘ [0] and works like this:

% iconv -f UTF-8 -t ISO-8859-1 old-utf8-file.txt > new-iso88591-file.txt

[0] http://www.gnu.org/software/libiconv/documentation/libiconv/iconv.1.html