Thanks. I tried, setting the exact same settings in fixed IP as were shown in the DHCP tab, and managed to make my ROCK unreachable 
I luckily had a USB keyboard nearby and managed to <RETURN>networkreset<RETURN> my way out of trouble without bricking my ROCK. I’m so glad the ROCK has that enabled; I’ve screwed up a couple other times in my network admin dilletantism and needed to get out of trouble but those devices had to be factory reset. This is much better. Will try again later.