Your understanding is correct. You can add the entries in the hostfile and then pull from it.
sample - /etc/rc
ifgrp create lacp INT-1G -b ip e0a e0b
ifgrp create single INT-10G e1a
ifgrp create single vif_second_level INT-1G INT-10G
ifgrp favor INT-10G
ifconfig vif_second_level `hostname`-vif_second_level netmask 255.255.255.0 mediatype auto partner vif_second_level
route add default 192.168.168.1 1
routed on
options dns.domainname abc.def.in
options dns.enable on
options nis.enable off
savecore
sample - /etc/hosts
127.0.0.1 localhost
192.168.x.25 filername-vif_second_level
192.168.x.20 mailhost
Ping the interfaces to ensure that the hosts are updated.
Reboot is NOT required. I mentioned source command, it is only required if you make any changes to the existing file or added new entry directly into the file and you want to reload the configuration in the memory without reboot. (This is b'cos any changes to /etc/rc file are effective on subsequent reboot)