Western Union Corp. extended the deadline for debt holders to exchange their debt for stock in a reorganized version of the company until midnight Thursday . . . Apple Computer Inc. said its directors approved the repurchase of up to 5 million of the firm's common shares . . . The FCC ordered Bell Atlantic and Southwestern Bell to refund more than $8.5 million to long-distance telephone companies, saying the two firms exceeded their authorized profit margin in 1985 . . . AM International Inc., Chicago, said Komori Printing Machinery Co., a Japan-based printing firm, has acquired 6.4%, or 3.3 million shares of AMI's common stock in open market transactions.