How do I update to a specific build? As of build 147, you can simply say
pkg install firstname.lastname@example.org.<buildid>
You may want to use the --be-name option to pkg install, or it will choose a name for the new boot environment for you. Prior to build 147, you have to do all the boot environment manipulation yourself. The canonical method is
pkg install SUNWipkg
beadm create newbe
beadm mount newbe /mnt
pkg -R /mnt install email@example.com.<buildid>
bootadm update-archive -R /mnt
beadm unmount newbe
beadm activate newbe
Note that for builds 133 and later, the name of the package delivering the packaging system has changed from SUNWipkg to package/pkg, so the latter should replace the former in the command sequence above and the discussion below.
Adding the entire package is necessary to keep your packages on versions that have been tested together; entire contains a series of constraint relationships that pkg(5) uses to make sure mutually compatible packages are installed on your system.