That would only change the LAN IP not WAN. Depends on what part of the router you are doing it on, most of the time I see it, it is on the WAN interface. Whether or not rebooting the router, or leaving it off overnight will help depending on how the ISPs equipment is set up. I work as a network engineer at a local ISP here, and I can tell you our routers hand out 24 hour leases. So if your lease doesn't renew overnight, then leaving it off overnight will not work for our equipment. Your router should have an option for "MAC address cloning" or something like that. Put in a different MAC address and restart the router and you should pull a new IP address, regardless of lease times. Ehm, just find that and put any random number?