Homeowners will no longer have to pay the Federal National Mortgage Assn. a conversion fee when converting a one-year adjustable-rate mortgage to a fixed-rate mortgage, the government-sponsored corporation says . . . Sports Shinko Co. of Osaka, Japan, and La Costa Hotel & Spa in Carlsbad, Calif. have signed a letter of intent to let SSC purchase the operating company that owns and operates the luxury resort for $250 million.