Sample with INPUT chain, before, issue the command
iptables -vL INPUT --line-number
you will have a look about the existing rules an their exact position (including the LOG’s rules) , then assume that you want to add a rule in the 20th line , so
iptables -I INPUT 20 ..... ....... ....... ........ ...... -j ......
You could add the command in Startup/Cron , Firewall Chain, so, even after a reboot, you’d find the rule applied. Remember that this rule , will be applied always in the 20th position, so you could have to adjust the script if you will remove or add some rules via gui, which are above the newest one inserted by the script.
It should work…