Changing Domains

I want to make a PDC of one domain(TEMP), a BDC on another domain(MAIN) without having to reload NT 4.0. Is this possible? The two domains aren’t connected. I want to try and demote the PDC to a BDC, and then change the domain name. I will have a wan link established between this server and the PDC of the other domain. I do not want to have to reload the server and have to physically move it to the MAIN domain. Any ideas? Is there a way to setup a modem connection before the NT 4.0 setup askes for the domain info, so that the BDC can find the PDC throught the modem connection?