/usr/local/etc/kea/kea-dhcp4.conf
Changing to ISC DHCP will be a real pain in the a.... as I have quite a lot of static leases and I can´t find any good way to export from KEA DHCP and import into ISC DHCP other than just open two GUI sessions and start copy/past between.
I was looking for this also. Personally I'm waiting (hoping?) for it to be added, as the Kea integration seems pretty raw currently. (Also doesn't seem to integrate reservation hostnames with DNS forward/reverse lookup?)Anyway, if you're more ambitious there was info here for options in Kea:https://kea.readthedocs.io/en/kea-2.2.0/arm/dhcp4-srv.html#custom-dhcpv4-optionsAnd the config files in Opnsense seem to be in /usr/local/etc/kea , although I'm not sure if edits would persist through changes via the UI.