B737 FLT CREW DOES NOT CORRECT CROSSING RESTRICTIONS ON CHINS 5 INTO SEA FOR NORTH FLOW AFTER RWY CHANGE; WHEN FMC IS PROGRAMMED FOR SOUTH FLOW.

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WE FAILED TO NOTICE THAT SEATTLE HAD CHANGED TO A N FLOW FOR LNDG. WE PROGRAMMED THE FMS/CDU FOR S FLOW. THIS RESULTED IN US XING RADDY INTXN AT 16000 FT RATHER THAN 12000 FT. ATC NOTICED THAT WE WERE UNUSUALLY HIGH ON OUR ARR AND ASKED IF WE WERE SET UP FOR N FLOW. WE ADMITTED OUR ERROR TO ATC. ATC INFORMED US THAT NO CONFLICT EXISTED; AND TO CONTINUE OUR APCH. WE WERE ABLE TO COMPLY WITH ALL OTHER ALT/SPD RESTRS ON THE ARR. THIS ERROR RESULTED FROM LACK OF ALERTNESS. WE BOTH FAILED TO NOTICE THAT SEATTLE HAD CHANGED TO N FLOW; AND BRIEFED THE ARR BASED ON S FLOW. THE ERROR WAS CORRECTED EARLY ENOUGH TO ALLOW A NORMAL DSCNT AND APCH TO THE ARPT. FLT CREW MUST BE ALERT AT ALL TIMES. ALWAYS CHK AND DOUBLE-CHK IMPORTANT ITEMS LIKE ALT RESTRS. ALWAYS MAKE SURE WE HAVE THE MOST UP-TO-DATE INFO; LIKE CURRENT ATIS. SUPPLEMENTAL INFO FROM ACN 765245: THE FMS WAS PROGRAMMED IN ADVANCE FOR S FLOW ON THE CHINS 5 ARR AND WE FAILED TO DOUBLE-CHK THE ALT RESTR FOR N FLOW AFTER SWITCHING. AFTER ZSE NOTICED WE WERE HIGH AT RADDY; THEY COMMENTED ON WHETHER WE HAD COPIED THE 'CHINS 5 LNDG N' CLRNC. WE ADMITTED OUR ERROR AND VERIFIED WITH ATC THAT NO CONFLICT EXISTED. THIS ERROR WAS DUE TO LACK OF ALERTNESS. NO CONFLICT EXISTED WITH APCH CTL AND WE CONTINUED OUR DSCNT EXPEDITIOUSLY FOR A NORMAL APCH TO RWY 34C. WE SHOULD HAVE BEEN MORE ON TASK AND DISCUSSED THE ARR MORE IN DEPTH; ESPECIALLY IN REGARDS TO RWY USE RELATIVE TO ALT RESTRS.