A couple of sections of my site are not completed yet and do not have a link to those section. I'm generating a sitemap of 50K urls, which as you may guess is very time consuming. Later, when I get those other sections of my site ready and enable the link to them, I'd like to map those sections without having to do the entire 50K already completed, but I'm afraid if it might overwrite sitemap.xml, rather than adding the new urls. Am I safe from that or should I do something different? Or do I have to generate the entire thing all over.