You might look at
http://forum.hauptwerk.com/viewtopic.php?f=4&t=14993&p=112035&hilit=+changing+midi+#p111950
This procedure did work for me.
You must keep the old name of the device present when you start HW (take the option to keep devices which are offline when you start) and you need to enable the "new device" so HW sees both the old name (which is offline) and the new name.
You need to do this for each sample set.
You should take a HW backup first!
Good luck.
Iain