config-example.xml

        <events>
            <m2epro_insert_attributes_pattern>
                <observers>
                    <sr_m2epro_insert_attributes_pattern>
                        <type>singleton</type>
                        <class>my_m2e_addon/observer</class>
                        <method>modifyAttributeSearchPattern</method>
                    </sr_m2epro_insert_attributes_pattern>
                </observers>
            </m2epro_insert_attributes_pattern>
            <m2epro_get_attribute_value_before>
                <observers>
                    <sr_m2epro_get_attribute_value_before>
                        <type>singleton</type>
                        <class>my_m2e_addon/observer</class>
                        <method>returnAttributeCodeBefore</method>
                    </sr_m2epro_get_attribute_value_before>
                </observers>
            </m2epro_get_attribute_value_before>
            <m2epro_get_attribute_value_after>
                <observers>
                    <sr_m2epro_get_attribute_value_after>
                        <type>singleton</type>
                        <class>my_m2e_addon/observer</class>
                        <method>returnAttributeCodeAfter</method>
                    </sr_m2epro_get_attribute_value_after>
                </observers>
            </m2epro_get_attribute_value_after>
        </events>

observer-example.php

<?php
    public function modifyAttributeSearchPattern($observer)
    {
        $event = $observer->getEvent();
        $object = $event->getM2eproData();
        // added pipe "|"
        $object->setData('preg_match_all', '/#([a-zA-Z_0-9|]+?)#/');
    }
    
    public function returnAttributeCodeBefore($observer)
    {
        $event = $observer->getEvent();
        $object = $event->getM2eproData();
        $attributeCode = $object->getData('attribute_code');
        
        if ($attributeCode === '_related_products_') {
            $object->setData(array(
                'is_direct_output' => true,
                'value' => '<<< related products html >>>'
            ));
            return;
        }

        $attributeCode = explode('|', $attributeCode);
        $object->setData('attribute_code', $attributeCode[0]);
        if ($attributeCode[1]) {
            $object->setData('html_tag', $attributeCode[1]);
        }
    }
    
    public function returnAttributeCodeAfter($observer)
    {
        $event = $observer->getEvent();
        $object = $event->getM2eproData();

        $tag = $object->getData('html_tag');
        if ($tag) {
            $object->setValue('<' . $tag . '>' . $object->getAttribute()->getStoreLabel() . '</' . $tag . '>' . $object->getValue());
        }
    }