From Genunix

How to change hostname on Solaris system (S10+, IPv4 only)

1. Edit /etc/inet/hosts; Change all instances of the old hostname to the new hostname
2. Change contents of /etc/hostname.<interfacename> to match new hostname (Run 'ls /etc/hostname.*' to see the list of files that you may need to change)
3. Edit the "/etc/nodename" file to contain the new hostname
4. Run `dumpadm` to set the new 'hostname' path for the kernel dumps to be stored. This path includes the hostname (check /etc/dumpadm.conf for current settings)
   • (I'm not sure if this step is necessary, or if it gets done during a reboot.).
5. reboot