The registry (Verisign Registry for .com .net and .org) is the authoritive source for and maintains the IP address. When you change the IP address of a name server, the change should actually occur at the registry (glue record) level. Registrar whois should pull the current and correct IP from the registry (I say *should* because we all know how netsol registrar's whois works).
So changing the IP address is a somewhat easy task for domains in .com .net and .org (no experience with .info or .biz yet). Also, I'm not sure how each of the ccTLD's keep their info updated. Hopefully they just refer back to the glue records for the name servers in the verisign registry. Changing the host name is an entirely different matter. It is a brand new DNS host record at the registry level, so you need to update each domain that uses that DNS server individually. Regards, Bill
