Since SEOPress 2.1.8
To block robots.txt file editing from SEO -> PRO -> Robots, copy and paste this to your wp-config.php:
define('SEOPRESS_BLOCK_ROBOTS', true);
To block .htaccess file editing from SEO -> PRO -> htaccess, copy and paste this to your wp-config.php:
define('SEOPRESS_BLOCK_HTACCESS', true);