Maryland Democratic Party officials acknowledged yesterday that they have replaced their executive director but said the move is little more than a change in job titles. The party has replaced Joshua M. White with acting Executive Director Derek Walker, who had served as the party's communications director. Mr. White was reassigned some time last month to the job of political director. The reorganization comes as more evidence shows a state Democratic Party operative was involved in a "dirty tricks" campaign to smear the administration of Gov. Robert L. Ehrlich Jr., a Republican. However, party officials said yesterday that the job...