NEW YORK (Standard&Poor's) Aug. 17, 2012--Standard&Poor's Ratings Services today said that the U.S. Treasury's amendments to its Preferred Stock Purchase Agreements (PSPAs) with Fannie Mae (senior debt rated 'AA+/Negative') and Freddie Mac (senior debt rated 'AA+/Negative') do not immediately affect the ratings on their debt instruments. The preferred stock held by the U.S. Treasury is not rated by Standard&Poor's. Changes to the PSPAs include: An accelerated wind-down of the entities' investment portfolios--to a 15% annual reduction of the portfolios, versus 10% previously; A newly required annual plan to be given to their conservator, the Federal Housing Finance Agency (FHFA), detailing their progress in reducing taxpayer exposure to mortgage credit losses; and The elimination of