B747 FLC DEVIATES FROM CLRED ALT AFTER RECEIVING CONFUSING CLRNC IN LAX AIRSPACE.

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DSCNT TO LAX ON THE PARADISE 2 ARR. ENCOUNTERED MODERATE TURB. UNABLE TO USE AUTOPLT AND AUTOTHROTTLE DUE TO TURB. WE WERE UNFAMILIAR WITH THIS ARR. AT APPROX RIFFT INTXN; WE WERE ASSIGNED 12000 FT; THEN TOLD BY APCH THAT WE WERE BEING SWITCHED TO THE MUDDE 4 ARR. WE WERE GIVEN NO REASON FOR THIS AND QUICKLY TRIED TO RETRIEVE THIS NEW AND AGAIN UNFAMILIAR ARR FROM OUR BOOKS. I GOT THE ARR OUT BUT DUE TO HAND FLYING THE ACFT IN MODERATE TURB AND NAVING A DEMANDING STAR; I LEFT IT TO THE FO TO STUDY THE NEW STAR AND FIGURE OUT THAT IT WAS A CHANGE OF RWY WITH NO TRANSITION FROM OUR CURRENT ROUTING. SOON AFTER XING PARADISE VOR; AND ESTABLISHED ON THE PDZ 277 DEG RADIAL; WE WERE TOLD BY APCH THAT RWY 25L WAS OPEN AGAIN AND NOW CLRED TO CROSS ARNES INTXN AT 10000 FT. BELIEVING THIS TO BE A 'DSND NOW' CLRNC; THE FO SET 10000 FT ON THE ALT ALERT AND SAID 'CLRED TO 10000 FT.' I BEGAN DSCNT FROM 12000 FT TO 10000 FT. AT APPROX 11700 FT; SOCAL APCH SAID 'VIA THE PARADISE 2 ARR.' I THEN REALIZED THAT ON THIS STAR; WE WERE NOT GOOD DOWN BELOW 12000 FT UNTIL 'TEJAY' 4 DME FROM PDZ. I ADDED PWR; THE ACFT BOTTOMED OUT AT 11500 FT. I CLBED BACK TO 12000 FT. BY THIS TIME WE WERE PAST TEJAY AND WE CONTINUED THE ARR. THERE WAS NO CONFLICT THAT I WAS AWARE OF. 1) UNFAMILIAR WITH LAX ARRS. 2) HVY TURB. HAND FLYING; RELYING ON FO FOR INTERP OF PLATES. 3) LAST MIN SOMEWHAT CONFUSING INSTRUCTIONS FROM APCH CTL.