adding custom rules on pfSense not supported by webgui

CUSTOM_rules.inc-pfSense

<?php

// Add this file as:  /usr/local/pkg/CUSTOM_rules.inc
// pfSense will automatically add the rules defined here into the rules it loads in pf

require_once("util.inc");

function CUSTOM_rules_generate_rules($type) {
	// called by filter.inc when pfSense rules generation happens
	$rules = "";
	switch($type) {
	case 'nat':
		$rules .= "# CUSTOM NAT RULES \n";
		$rules .= "nat on em0 inet6 proto tcp from ! (em0) to any -> 123::456\n";
		$rules .= "# END CUSTOM NAT RULES \n";
		break;
	case 'filter':
		$rules .= "# CUSTOM RULES \n";
		$rules .= "# END CUSTOM RULES \n";
		break;
	}
	return $rules;
}

?>

hello,
It's awesome! I really need this code.
I would like to install tinc package on pfsense, but the default webUI configuration does not satify my need, I have to hack to add some custom rules. and I found your code.

two questions:

1. how to reference this function on /etc/inc/filter.inc?
2. any possible to delete the rules which generate from custom_rules.inc when some conditions meet.