Switch certain field headings in Omeka's custom_show_item_metadata function.

functions.php

<?php

function custom_show_item_metadata(array $options = array(), $item = null)
{
    
    $item = $item ? $item : get_current_item();

    if ($dcFieldsList = get_theme_option('display_dublin_core_fields')) {

        $otherElementSets = array();

        $elementSets = get_db()->getTable('ElementSet')->findForItems();
        foreach ($elementSets as $set) {
            if ($set->name == 'Dublin Core') continue;
            $otherElementSets[] = $set->name;
        }

        $html = '<h2>' . __('Dublin Core') . '</h2>';
        $dcFields = explode(',', $dcFieldsList);
        foreach ($dcFields as $field) {
            $field = trim($field);

            // Create $fieldLabel, change its value for certain fields.
            switch($field) {
                // Check if $field is 'Description'
                case 'Description':
                    $fieldLabel = 'Header'; // Change value to 'Header'
                    break;

                // Check if $field is 'Relation'
                case 'Relation':
                    $fieldLabel = 'Further Reading'; // Change value to 'Further Reading'
                    break;

                // Check if $field is 'Text'
                case 'Text':
                    $fieldLabel = 'Further Reading';
                    break;

                // Leave the default for headings you don't want to change.
                default:
                    $fieldLabel = $field;
            }

            if (element_exists('Dublin Core', $field)) {
                if ($fieldValues = item('Dublin Core', $field, 'all')) {

                    // Use $fieldLabel for heading
                    $html .= '<h3>'.__($fieldLabel).'</h3>';
                    foreach ($fieldValues as $key => $fieldValue) {
                        if (!item_field_uses_html('Dublin Core', $field, $key)) {
                            $fieldValue = nls2p($fieldValue);
                        }
                        $html .= $fieldValue;
                    }
                }
            }
        }
        $html .= show_item_metadata(array('show_element_sets' => $otherElementSets));
        return $html;
    } else {
        return show_item_metadata($options, $item); 
    }
}