Fannie Mae and Freddie Mac are scrambling to stay in a rapidly changing mortgage market that has seen an unexpected shift to adjustable-rate mortgages and new product designs in 2005. With the agency share of new MBS production slipping in 2005, all three secondary-market agencies are responding with new securitization projects. By virtue of their private corporate status, Fannie and Freddie have a huge advantage over Ginnie Mae in trying to adapt to the primary…