Overwriting a filter

OK so I generated this metabox which will be included in my theme:

function themename_page_options_metabox( $meta_boxes ) {
	$prefix = 'themename_';

	$meta_boxes[] = array(
		'id' => 'page-options',
		'title' => esc_html__('Hide Stuff','themename'),
		'post_types' => array('post','page'),
		'context' => 'side',
		'priority' => 'default',
		'autosave' => true,
		'fields' => array(
			array(
				'id' => $prefix . 'hide_stuff',
				'name' => esc_html__('Hide This','themename'),
				'type' => 'checkbox',
				'desc' => esc_html__('This is the description','themename'),
			),
		),
	);

	return $meta_boxes;
}
add_filter('rwmb_meta_boxes','themename_page_options_metabox');

So after they install the theme, they use a plugin that will add more choices. How would I overwrite the filter above to add more choices when the plugin is added and activated, like this:

function themename_page_options_metabox( $meta_boxes ) {
	$prefix = 'themename_';

	$meta_boxes[] = array(
		'id' => 'page-options',
		'title' => esc_html__( 'Hide Stuff', 'themename' ),
		'post_types' => array( 'post', 'page' ),
		'context' => 'side',
		'priority' => 'default',
		'autosave' => true,
		'fields' => array(
			array(
				'id' => $prefix . 'hide_this',
				'name' => esc_html__('Hide This','themename'),
				'type' => 'checkbox',
				'desc' => esc_html__('This is the description','themename'),
			),
			array(
				'id' => $prefix . 'hide_that',
				'name' => esc_html__('Hide That','themename'),
				'type' => 'checkbox',
				'desc' => esc_html__('This is the description','themename'),
			),
			array(
				'id' => $prefix . 'hide_and_the_other',
				'name' => esc_html__('Hide This, That and the Other','themename'),
				'type' => 'checkbox',
				'desc' => esc_html__('This is the description','themename'),
			),
		),
	);

	return $meta_boxes;
}
add_filter( 'rwmb_meta_boxes', 'themename_page_options_metabox' );