Overriding template view function in Django app.

[sonu kumar]

I have installed third party app(Mezzanine) whose urls are configured to use their view functions not View Class. Source code from mezzanine.blog.urls

       urlpatterns = patterns("mezzanine.blog.views",
   url("^%stag/(?P<tag>.*)%s$" % _slashes, "blog_post_list",
        name="blog_post_list_tag"),
    ...
)
As we can see they have configured blog URLs to use mezzanine.blog.views. Here we have few functions which are being called by URL dispatcher.  one of them is below.
       def blog_post_list(request, tag=None, year=None, month=None, username=None,
                   category=None, template="blog/blog_post_list.html",
                   extra_context=None):
    """
    Display a list of blog posts that are filtered by tag, year, month,
    author or category. Custom templates are checked for using the name
    ``blog/blog_post_list_XXX.html`` where ``XXX`` is either the
    category slug or author's username if given.
    """
I would like to override this function so that it will call my function to update context dictionary  or pass some more arguments to default function blog_post_list (it's having an argument extra_context so we can use this as external context) 

How can I achieve this ?
 Please provide complete details like do we have to modify urlpatterns then what should be changed, if we have to change view then what should be change ?