How does VS 2013 effect a class ASP application?

I've done some contract work for a friend of mine, who has a large classic ASP website he manages and maintains. He uses Microsoft Expression Web 4 to maintain it, and when I help him I also use Expression Web 4. I did classic ASP way back in the day, so yes I can do it, but honestly I'd rather not. I'd rather use ASP.NET Web Forms or ASP.NET MVC. But I'm very concerned with what might happen to the meta data maintained by Expression Web, if I were to open it in VS 2013.
What effects would VS 2013 have on a classic ASP app to the meta data used by Expression Web 4? If I were to open this large classic ASP application in VS 2013 would it ruin the meta data used by Expression Web 4 so that it couldn't open it or make it inconsistent?