The setvar/printvar capabilities in the CBoot console are pretty limited. You can currently only update/show the vars in the CBO (CBoot Boot Options) feature (cbo.dts), such as:
boot-order
dhcp-enabled
boot_pt_guid
static-ip
tftp-server-ip
ip-netmask
ip-gateway
See the T194 CBoot source, tegrabl_cbo.c and var_cmd.c in particular.
This was going to replicate the functionality in U-Boot, as @linuxdev says, but never got fleshed out much more than printing/changing the CBO variables.
HTH,
Tom