Perl can be used to do any sort of system work. You don't say what sort of network management you use besides DHCP, so it's hard to suggest code for this. Anything you can do from the shell can be done from perl with system and friends.

What do you do about a multiuser box?

To successfully enter a web interface, the user's network interface has to already have an IP address that works. Why change it?

In fundamental terms, IP's represent network interfaces, not machines or users. It sounds like you're putting the cart before the horse somewhere to generate this project.