Example migrated from Codex:

An example of adding new endpoint to Rewrite Rules.

function site_custom_endpoint( $wp_rewrite ) {
    $feed_rules = array(
	  'my-account/?$' => 'index.php?account-page=true',
	  'my-account/edit-profile/?$' => 'index.php?account-edit-profile=true',
    );

    $wp_rewrite->rules = $feed_rules + $wp_rewrite->rules;
    return $wp_rewrite->rules;
}

add_filter( 'generate_rewrite_rules', 'site_custom_endpoint' );