Some OSs (Win2000/XP) may check the volume ID (which is
AFAIK set by Format and unchanged by Xcopy/Xcopy/Ghost) and complain if this doesn't match what they expect.
Mark Russinovitch's freeware "VolumeID" from
http://www.sysinternals.com/ntw2k/source/misc.shtml allows you to change the volume ids of FAT and NTFS disks under Windows NT, Windows 2000, and Win9x. Useful to Windows NT admin. [You could use a disk sector editor to do the same thing]
"While WinNT/2K and Windows 9x's built-in Label utility lets you change the labels of disk volumes, it does not provide any means for changing volume ids. This utiltity, Volumeid, allows you to change the ids of FAT and NTFS disks (floppies or hard drives) on both Windows NT/2K and Windows 9x."
I don't know, but it is possible that these OSs may get confused if they see two volumes with the same ID on bootup so you may have to juggle things a bit (maybe not).
Don't change the Volume ID if you don't have to.
[Edited to add that for those who don't know, you can see the Volume ID by typing Vol<Enter> at a command/DOS prompt. M$ refers to it as the Volume Serial number and it is in the hex format xxxx-xxxx (eg 3C5A-18D6 for my main drive) - I think that it is statically derived from the date/time when the drive is formatted.]