When you would try to change the filepermission with a php script on your hosting, you would probably run into an "Operation not permitted" error.
This is because save mode is enabled. To bypass this limitation you could login unter ftp and change the file permission from there.
PLAIN TEXT
PHP:

//settings

$folders = array("/feeds/","/sitemap/");

$ftp_details['ftp_user_name'] = "username";

$ftp_details['ftp_user_pass'] = "pw";

$ftp_details['ftp_root'] = [...]