Some religious copycats, apparently recalling self-named "Captain Midnight's" one-time satellite piracy, foisted their particular message in a similar manner. Officials of the Playboy Channel Tuesday said a printed message reading "Repent your sins . . . Keep the Sabbath holy" appeared for 10 to 15 seconds on cable subscribers' TV screens in Oklahoma and Texas Sunday night. Officials are now trying to determine just how many viewers of their adult cable television programming saw the unauthorized message. The Federal Communications Commission doesn't take such illegal activity lightly: "Captain Midnight" (real name: John MacDougal), who broke into the satellite feed of HBO in 1986 with his own message, was fined $5,000 and put on one year's probation for his prank.