[Zope-CMF] What's the CMF way to override a method

[Loren Stafford]

I don't like the way CMFDefault.File.download works. So, I want to override
it with my own method in a simple way that will not be undone by upgrading
to future releases of CMF. I know I can create a new factory type derived
from File, but that seems like overkill. I looks like I could somehow use
the /Portal/portal_types/File Action tab, but I haven't succeeded.

There must be a simple way to do this. Could somebody point me in the right
directions?

-- Thanks
-- Loren