WordPress at a glance
filter is not described

customize_load_themes filter-hook . WP 4.9.0

Filters the theme data loaded in the customizer.

This allows theme data to be loading from an external source, or modification of data loaded from wp_prepare_themes_for_js() or WordPress.org via themes_api().

Usage

add_filter( 'customize_load_themes', 'filter_function_name_2011', 10, 3 );
function filter_function_name_2011( $themes, $args, $manager ){
	// filter...

	return $themes;
}
$themes(array)
Nested array of theme data.
$args(array)
List of arguments, such as page, search term, and tags to query for.
$manager(WP_Customize_Manager)
Instance of Customize manager.

Where the hook is called

WP_Customize_Manager::handle_load_themes_request()
customize_load_themes
wp-includes/class-wp-customize-manager.php 5530
$themes = apply_filters( 'customize_load_themes', $themes, $args, $this );

Where the hook is used (in WP core)

Does not used.