Is there any reason this wouldn't work (haven't tried it with earlier builds) when pasting into the System Commands window and executing?:
nvram set lan_ipaddr="192.168.2.1"
nvram set dhcpd_startip="192.168.2.100"
nvram set dhcpd_endip="192.168.2.149"
After executing, it gives me a nondescript error (ERROR: unknown). It seems to reboot the router, but none of the settings stick.
Just for my own sanity, I tried this with the same outcome: