Multiple domain names
I have A VDSL modem for internet acces, it has its own domain name say abc.com. If I set my own domain name say xyz.com server and setup dns server for xyz.com domain controller and dhcp server on separate server, now what should I do with modem domain name abc.com? should I change it to xyz.com or do some thing else.
A modem cannot have a domain name, but a router can. So, if your question is can you access the router and at the same time port forward to a server using HTTP, then no, you will will lose being able to connect to the router via HTTP.
If this does not answer the question then please be more specific.