Instead of always specifying to use DHCP when issuing the boot command, you can save the instruction at the PROM level by setting up an NVRAM alias.
For example, the following instruction sets a system to use DHCP when booting from a network device.
ok nvalias net /pci@1f,4000/network@1,1:dhcp
When you subsequently boot the system, instead of typing boot net:dhcp, you would only type boot net.
Caution - Do not use the nvalias command to modify the NVRAMRC file unless you are very familiar with this command as well as with the nvunalias command.