Force the merge duplicate venues and organizers button to appear (The Events Calendar 4.6: Events > Settings > General screen)

force-merge-button.tec.4.6.3.php

<?php
/**
 * Force the merge duplicate venue/organizer button to appear.
 *
 * Written for TEC 4.6.3, may or may not work with other versions.
 *
 * @param mixed  $value
 * @param mixed  $default
 * @param string $key
 *
 * @return mixed
 */
add_filter( 'tribe_get_single_option', function( $value, $default, $key ) {
    return 'organizer_venue_amalgamation' === $key ? 0 : $value;
}, 10, 3 );