Custom event category page titles sample

add_filter('the_title', 'change_event_category_title', 10, 2);

/**
 * Note - deliberately not using tribe_is_event_category() with TEC 3.0.3 as it can return
 * true even if no particular category has been selected.
 */
function change_event_category_title($title, $id) {
    if (-9999 !== $id || !tribe_is_event_query()) return $title; // Leave non-Tribe pages untouched
    if (!$GLOBALS['wp_query']->tribe_is_event_category) return $title; // We're only interested in archives
    return 'Custom Event Archive Title'; // Build your custom title (perhaps manipulate $title)
}