Well, that's simple. When you login via the console (ssh, for example), simply run "setup appliance nmc edit-seettings". You can tab your way through that command as well. Once there, go and edit expert_mode to be "1". Yes, you've enter the "vi" command zone, so save and exit with ':wq'
Once the changes are saved, you'll be asked to refresh the console settings, and now you can type "!bash" to get a nice usable shell, or bang escape any command. You'll be root, so, be aware and behave! Now you know what Nexenta Core was all about, as its all there at your fingertips, along with NMS, NMC, and NMV subsystems that are the foundation of the NAS product.
I was told that an alternative way to set expert mode is
option expert_mode = 1 -sas denoted in the "option -h" documentation for NMC. The "-s" flag updates the on-disk configuration.