>It's more than that; it's downright suicidal to do. There is more than one place in the system where the change is going to be recorded, it's goingto force a reboot (not just a logout) and if you duplicate a functioning IP address as a result, at a minimum the node is going to drop from the net...

If it was in the same subnet, it'd probably cause BOTH machines to drop off the net. If it was separated by a router, the craziness would be more subtle and require more time/effort/expensive tools to discover.

The only application (other than illegal/immoral stuff) would be a major network overhaul, where you're moving statically assigned IP's to a DHCP server. If you could launch the re-IP program from a login script, it would automate the process for a lot of machines. Even this is a scary thought. If it didn't work *perfectly* then it'd double (or worse) the amount of time to fix as to just perform the operation manually.