We frequently use the printenv command to display the NVRAM's variables, its user defined values and its default values. Here's an example of changing the boot device.
Open Boot Prom (OBP) mode ok printenv (You might have a PROM password set. If so, you will have to enter it.) setenv boot-device disk1
By the way, the eeprom command can do the same (set boot device) thing in the init 3 level.