Although you don't specify what the program is to be, nor what exactly the
local prservationists deem "impossible" it certainly sounds like you could be
involved in something really great.  Please elaborate, and on what ideas
you're looking for, in the meantime, I'll blather on for a bit.

I'm assuming that the original building has merit, even if not aesthetic,
there obviously is a lot of local interest in 'their' building.  We do have a
tendency in the US to assume anything old is good - some interesting notes on
that by Christopher Chippendale (a British archaeologist) in I think,
Antiquity from the early 1990's.

England and Italy come to mind as two countries which have maintained either
maintained shells of their historic buildings or merged the two.  The
juxtaposition of old and new brings to mind that Carlo Scarpa project ( the
something or other museum) which personally, although I've never visited it
appears to be a great interweaving of new elements into the existing fabric
(although accessibility is a challenge at his projects) A project that I did
visit, was the the new Sainbury wing in London which although not necessarily
my taste, certainly presents an addition very much in the feeling of the
existing building while not replicating the historical detailing.  Anyway,
there many examples and I think it's a really important subject - that one can
acknowledge the past while recognizing that while some needs and behaviours
are the same as those of 100 years ago, that others have changed.   And theere
is nothing wrong in reflecting that - both in the spatial organization and
complementry construction and details.  After all, we do tend to think of
historic buildings as frozen in a certain time period rather than as evolving
and changing pieces.    My perspective comes out of archaeology, generally
pre-hsitoric, my previous field, so I do take a longer term approach to
historic buildings, as I tend to view thing within a larger framework.

Anyway, keep posting on this villa