linux – How to safely change CentOS 7 hostname without risking main website downtime?

Sorry, a newbie here with a silly question. My CentOS7 server admin setup the server with my main domain (web site) as a root. Now I would like to add another domain to the same server, what is the best way to go? Do I need to create a new user, or I could do it as root again? Thanks in advance!

I’ve tried to do it on my own and learn Linux, but after plenty of Googling I still couldn’t find the safe way to do it on my own without a high risk of ruining the current setup which would put my main website offline. Thank you in advance