A320 FLT CREW IS CHANGED FROM RWY 24R TO RWY 25L WHILE ON THE SEAVU1 ARR TO LAX. THE CHANGE DOES NOT GO SMOOTHLY AND THE FLT CREW ENDS UP RECEIVING ALT AND HEADING ASSIGNMENTS FROM SCT ALONG WITH A PHONE NUMBER TO CALL.

Narrative

ON THE SEAVU RNAV STAR; WE WERE SET UP FOR THIS ARR MERGING INTO RWY 24R ILS APCH; WITH RWY 25L IN THE SECONDARY FLT PLAN IN THE FMS. WE WERE DSNDING ON THE ARR IN TO LAX MAKING THE CROSSING RESTRS WHEN WE WERE GIVEN RWY 25L INSTEAD. THE CAPT WENT TO ACTIVATE THE SECONDARY FLT PLAN WITH RWY 25L FOR ME AND HE PUNCHED THE WRONG BUTTON AND IT WAS CANCELLED INSTEAD. HE IMMEDIATELY BEGAN TO PUT IT BACK IN BUT TOOK TWO OR MORE TIMES TO GET IT IN CORRECTLY AGAIN. BY THIS TIME WE HAD OVERSHOT THE NOW CLOSER ENTRY POINT SLIGHTLY. ATC NOTICED WE HAD NOT MADE THE TURN AND GAVE US A HEADING TO INTERCEPT THE LOC FOR RWY 25L. THE ONLY PROBLEM IS THAT THE FMC BOX MUST BE LOADED CORRECTLY TO HAVE THE FREQUENCY CHANNEL IN PROPERLY. ANOTHER HEADING AND ALTITUDE TRANSMISSION WAS REQUIRED. TO DIAL IT UP MANUALLY AT THIS TIME WOULD BE TIME CONSUMING. ANYWAY; WE SHOULD HAVE TOLD ATC SOONER WE WERE HAVING A PROBLEM WITH THE RWY CHANGE; BUT IT SEEMED IT WAS ONLY A SECOND OR TWO AWAY FROM GETTING IT FIXED EACH TIME THE CAPT TRIED. WE WERE GIVEN A PHONE NUMBER TO CALL; WHICH WE DID; AND THEY WANTED TO KNOW WHAT THE DEAL WAS AND WE EXPLAINED WHAT HAPPENED. IT WAS OK WITH THEM THEN. NO HARM NO FOUL THEY SAID. THESE ARRIVALS AND RWY SPECIFIC ROUTINGS CAN BE TRICKY IF NOT DONE RIGHT. HAVING TO CHANGE SO LATE IN THE WHOLE DEAL IS NOT GOOD. PROPER TIME TO BRIEF THE NEW APCH AND MONITOR THE TRANSITION FROM ARR TO APCH SEGMENT IS LIMITED ESPECIALLY IF SOMETHING GOES WRONG IN THE SWITCH OVER; AS IT DID WITH THIS ONE. I WILL BE VERY MUCH MORE ON THE ALERT THE NEXT TIME. NO TRAFFIC CONFLICTS OCCURRED.