(Source: https://knowledge.autodesk.com/support/smoke/learn-explore/caas/sfdcarticles/sfdcarticles/Setting-the-Mac-hostname-or-computer-name-from-the-terminal.html)

Procedure

Perform the following tasks to change the workstation hostname using the scutil command.

1. Open a terminal.
2. Type the following command to change the primary hostname of your Mac:
   This is your fully qualified hostname, for example myMac.domain.com
   sudo scutil –set HostName <new host name>
3. Type the following command to change the Bonjour hostname of your Mac:
   This is the name usable on the local network, for example myMac.local.
   sudo scutil –set LocalHostName <new host name>
4. Optional: If you also want to change the computer name, type the following command:
   This is the user-friendly computer name you see in Finder, for example myMac.
   sudo scutil –set ComputerName <new name>
5. Flush the DNS cache by typing:
   dscacheutil -flushcache
6. Restart your Mac.