[Event Manager] Formatting Month Title in Event List Grouped

Using Event Manager 5.2.9 on WordPress 3.4.2.
I have an event list grouped by month. I want to be able to custom format the month title in a way that is update safe. Currently, I edit em-template-tags.php changing this:
echo ‘<h2>’.$month.'</h2>’;
to this:
echo ‘<h2 class=”month-title”>’.$month.'</h2>’;
And then defining “month-title” in my theme’s style.css.

The problem is that this change will not survive an update. Is there a better way to do this?

Example of page at http://www.tuj.org/calendar

Thanks

Steve