add_filter( 'vcex_blog_grid_media', function( $output, $atts ) {

	if ( isset( $atts[ 'classes' ] ) && 'mycustom-classname' == $atts['classes'] ) {
		if ( $secondary = get_post_meta( get_the_ID(), 'wpex_secondary_thumbnail', true ) ) {
			$secondary_image = wpex_get_post_thumbnail( array(
				'attachment'    => $secondary,
				'size'          => isset( $atts['img_size'] ) ? $atts['img_size'] : '',
				'width'         => isset( $atts['img_width'] ) ? $atts['img_width'] : '',
				'height'        => isset( $atts['img_height'] ) ? $atts['img_height'] : '',
				'crop'          => isset( $atts['img_crop'] ) ? $atts['img_crop'] : '',
				'class'         => 'vcex-blog-entry-img',
				'apply_filters' => 'vcex_blog_grid_thumbnail_args',
				'filter_arg1'   => $atts,
			) );
			return '<div class="vcex-blog-entry-media entry-media"><a href="' . esc_url( get_permalink() ) . '" title="' . esc_attr( get_the_title() ) . '">'. $secondary_image . '</a></div>'; // override media with first image
		}
	}

	return $output;

}, 10, 2 );