Not necessarily totally safe! I think it will be okand not show if you use a separate file from /etc/dnsmasq.d/dhcp.conf, but if you used /etc/dnsmasq.d/dhcp.conf I'd expect it to try to show up in the webconfig in the TFTP section and would show with an error as it only accepts an IP address. The webconfig generally reads the underlying files directly and just displays values it sees there. I would expect it to parse the /etc/dnsmasq.d/dhcp.conf file and show an option 66 entry as TFTP. Note this is all guesswork based on experience rather than an ability to read the webconfig code.

Nick,
Thanks a lot for the info. Is it safe to assume any changes like this that I make via dnsmasq will NOT show up in the gui?
Just thinking about those who might have to access this system after me.

Hello and welcome to ClearOS.

DHCP in ClearOS is handled by dnsmasq. Google "dnsmasq option 66". It is best to add any manual options to a new file called anything you want in /etc/dnsmasq.d/ then reload dnsmasq with a:

systemctl restart dnsmasq.service

My concern is that setting it will interfere with the ClearOS webconfig, so, at a minimum, do not set the option by editing /etc/dnsmasq.d/dhcp.conf