custom_emoji.php

<?php
require_once('emoji.php'); // Provides a $GLOBALS['emoji_maps'] etc..

function emoji_unified_to_code($text){
	return preg_replace_callback($GLOBALS['emoji_maps']['unified_rx'], function($m){
		if (isset($m[2]) && $m[2] == "\xEF\xB8\x8E") return $m[0];
		$cp = $GLOBALS['emoji_maps']['unified_to_html'][$m[1]];
		return "[emoji{$cp}]";
	}, $text);
}

function emoji_code_to_unified($text){
	return preg_replace_callback("!\[emoji([0-9a-f]+)\]!", function($m){
		if (isset($GLOBALS['emoji_maps']['html_to_unified'][$m[1]])){
			return $GLOBALS['emoji_maps']['html_to_unified'][$m[1]];
		}
		return $m[0];
	}, $text);
}
?>