Freddie Mac, the nation’s No. 2 mortgage finance company, replaced its top three executives this week in the wake of an accounting investigation. The company’s president was accused of not fully cooperating with auditors reviewing the company’s 2000-2002 financial statements.Update 6-11-03: In spite of attempts to control damage, the mortgage giant now faces even greater scrutiny. Results of an informal probe of the company, begun by the Securities and Exchange Committee (SEC) in January, 2003, has prompted a formal investigation. Additionally, the U.S.