They do this where I work, but they have it as a part of everyone's NT logon script so that if you were to go into the registry and delete the keys the next network login would automatically put the message back. In addition to that they use the NT login script to modify the registry to have any computer that connects to the network automatically enabled to support multiple users and also somehow disable regedit.

The one thing that I don't like about the way this is implemented where I work is that if you connect to the company's network from your own machine at home, say through VPN, when you log in to the network the NT logon script updates your personal machine. I raised heck about this to our network admin who blew me off saying for me to quit connecting that way if I didn't like it.

I feel that they quasi-hacked my machine at home by updating my registry without my knowledge, so I had the admin forced to clean my registry and supply me with a laptop to take home.