100% to 50%:
ssh root@ip.ad.re.ss "/etc/init.d/bosminer_monitor stop && sed -i 's/fan_set_duty(i, 100)/fan_set_duty(i, 50)/g' /usr/sbin/bosminer_monitor.lua && /etc/init.d/bosminer_monitor start"
At your own risk...
I tried, and it made no difference. Fans spin up to 100% when bosminer is restarted or device starts up/
I even tried at 25% and there was no difference.
http://prntscr.com/218qha3