How change a disk's UUID without erasing it?

A fellow in the Apple Time Machine forums was having trouble with Time Machine using different external HDs for backups. Turns out, he had 3 WD drives with the same UUID!

I always thought that was impossible, but it was true, and does explain why TM used the first of the 3 that it found.

According to the MAN page for hfs.util, option -s should assign a new UUID; but it doesn't. It doesn't throw an error message, either.

http://developer.apple.com/mac/libra...fs.util.8.html

I posted in the Apple UNIX forum, to no effect.

Anybody know how to do this (and why hfs.util doesn't work)?