B777 CREW LEARNS THE COMPLEXITY OF CHANGING RWYS ON THE CIVET5 INTO LAX.

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ATC IS CHANGING TOO MANY APCH PARAMETERS WITHIN TOO LITTLE SPACE TO SAFELY AND WITHIN REASON COMPLY. WE WERE CLEARED TO LAX VIA THE CIVET5 BY LAX CENTER. WE HAD APCH CLEARANCES STARTING WITH THE CIVET5 FOLLOWED BY THE CIVET RWY 24R FOLLOWED BY THE CIVET RWY 24L FOLLOWED BY THE RWY 24L ILS. ALL THESE CLEARANCES WERE GIVEN TOO CLOSE TO CROSSING FIXES REQUIRING ALT RESTRICTIONS. BY THE TIME A NEW ARR WAS ISSUED AND ENTERED INTO THE FMC THE NEXT FIX WAS UPON US. NOT ONLY DID THIS COMPOUND THE WORKLOAD BUT THE FMC IS NOT USER FRIENDLY WHEN CHANGING THE CIVET ARR. DIFFERENT RWY AND TRANSITION FIXES FROM THE ILS AND THE ARR ITSELF NEED TO BE INPUT AND VERIFIED. ATC IS JAMMING THIS AT A BAD TIME DURING THE APCH. I DON'T KNOW WHAT HAPPENED TO THE ORIGINAL CIVET BUT THIS IS A GIANT MESS. I SUGGEST IF THIS IS TO CONTINUE THEN ANYONE COMING TO LAX SHOULD RUN THIS SCENARIO ON RTE 2 TO PRACTICE. WHEN YOU TRANSITION FROM THE CIVET RWY 24R TO CIVET RWY 24L YOU GET A BLANK DISCONTINUITY THAT REQUIRES A TRANSITION FROM THE FIX BEHIND YOU; EITHER PGS OR HEC WHEN ARRIVING FROM THE EAST. OTHERWISE YOU LEAVE A BLANK ON THE ND WITH NO LNAV. DOUBLE CHK WHICH TRANSITION COLUMN YOU ARE USING AND VERIFY THAT THE FIX IS BEHIND YOU TO GET THE REQUIRED RUSTT OR GRAMM OR CIVET IN FRONT OF YOU ON THE DISPLAY. WE DID IT...FINALLY. TO MAKE THIS CLEAR AS MUD WHEN ATC CHANGES THE CIVET CLOSE IN YOU HAVE TO RESELECT THE ARR AND THE TRANSITION THAT YOU HAVE PASSED OVER MANY MILES AGO TO GET THE CORRECT FIXES TO SHOW UP IN FRONT OF YOU...JUST BE CAREFUL SELECTING THE CORRECT TRANSITION COLUMN ON THE FMC.