Import WordPress Customizer settings when a theme is activated.

functions.php

/**
 * This function assumes you have a Customizer export file in your theme directory
 * at 'data/customizer.dat'. That file must be created using the Customizer Export/Import
 * plugin found here... https://wordpress.org/plugins/customizer-export-import/
 */
function import_customizer_settings()
{
	// Check to see if the settings have already been imported.
	$template = get_template();
	$imported = get_option( $template . '_customizer_import', false );
	
	// Bail if already imported.
	if ( $imported ) {
		return;
	}
	
	// Get the path to the customizer export file.
	$path = trailingslashit( get_stylesheet_directory() ) . 'data/customizer.dat';
	
	// Return if the file doesn't exist.
	if ( ! file_exists( $path ) ) {
		return;
	}
	
	// Get the settings data.
	$data = @unserialize( file_get_contents( $path ) );
	
	// Return if something is wrong with the data.
	if ( 'array' != gettype( $data ) || ! isset( $data['mods'] ) ) {
		return;
	}
	
	// Import options.
	if ( isset( $data['options'] ) ) {
		foreach ( $data['options'] as $option_key => $option_value ) {
			update_option( $option_key, $option_value );
		}
	}
	
	// Import mods.
	foreach ( $data['mods'] as $key => $val ) {
		set_theme_mod( $key, $val );
	}
	
	// Set the option so we know these have already been imported.
	set_option( $template . '_customizer_import', true );
}

add_action( 'after_switch_theme', 'import_customizer_settings' );

Thanks for this code, it's helping on a current project - FYI error in line 46, the function to call is update_option not set_option