For the first list I think you're just looking for a regex that does NOT match the category you want to exclude. I haven't tested this, but try the regular expression 

    ^(?!13)$
So you would end up with:

    {exp:stash:get_list name="articles" match="#^(?!13)$#" against="category_id"}
    ...
to see if that finds all items in your articles list that are not category 13.