Good question. I can’t speak as to why the options are grayed out (it’s been a long time since I was last a Dreamweaver user) but there are no restrictions in the file in terms of what you can or can’t edit. Any of it can be changed by the user if you’d like to.
I’ve personally been a big fan of Espresso because it has the best live editing of CSS that I’ve tried. I like being able to see the changes I’m making as I make them.