[Plugin: Pronamic Google Maps] Mashups: How to display description in the popup box

Yes, there is a way:

function prefix_pgmm_item($itemContent) {
	$itemContent = '';
	$itemContent .= '<h2>';
	$itemContent .= '	<a href="'. get_permalink() .'">';
	$itemContent .= '		'. get_the_title();
	$itemContent .= '	</a>';
	$itemContent .= '</h2>';
	$itemContent .= '<h3>Address</h3>';
	$itemContent .= wpautop(get_post_meta(get_the_ID(), '_pronamic_google_maps_address', true));
	$itemContent .= '<h3>Description</h3>';
	$itemContent .= wpautop(get_post_meta(get_the_ID(), '_pronamic_google_maps_description', true));

	return $itemContent;
}

add_filter('pronamic_google_maps_mashup_item', 'prefix_pgmm_item');

Problem is with that, when we update the plugin, changes are gone.
Is there is a way to rewrite the output without touching to the plugin core code ?

You can add the code above in your own theme or plugin.