ACR WDB ALT DEVIATION OVERSHOT DURING DESCENT AND COMPLAINT ABOUT FREQUENT RWY CHANGES WHEN LNDG LAX.

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ON A HDOF TO LAX APCH CTL WE WERE TOLD TO DSND TO 8000' AND INTERCEPT FLY IN ON THE LAX RWY 25L LOC. THE NEW APCH CTLR CHANGED OUR CLRNC TO INTERCEPT THE RWY 24R LOC WITH A HDG TO INTERCEPT. IN FEW MINS LATER HE CALLED BACK TO GIVE US A LOWER ALT AND ALSO REQUESTED OUR PRESENT ALT; WHICH THE F/O READ TO HIM AS 9300'. HE REPLIED THAT HE HAD GIVEN US 10000' AS AN ALT. WE TOLD HIM THE PREVIOUS CTLR HAD CLRED US TO 8000' AND WE DID NOT HEAR OR READ BACK THE RESTRICTION OF 10000'. HE TOLD US THERE WAS 'NO PROB;' AND CLRED US TO LOWER. I UNDERSTAND THE TFC PROBS AND RESTRICTIONS AT LAX ARE TOUGH ON CTLRS; BUT AT LAX; MORE SO THAN ANY OTHER HIGH DENSITY TCA'S I FLY INTO; THERE IS W/O A DOUBT MORE AIRSPD CHANGES; ALT RESTRICTIONS AND MORE IMPORTANTLY; RWY CHANGES THAN ANY OTHER AREA. I HAVE SEEN; ON ANOTHER OCCASION; A TOTAL OF 6 CHANGES TO OUR RWY ASSIGNMENT AT LAX; WHICH IN IMC OR MARGINAL (SMOGGY) VMC DAYS REQUIRES A CHANGE OF APCH PLATES; MINIMUMS BUGS; FREQS; ETC. THIS IS WHAT WAS GOING ON AT THE TIME OF THIS RPTED INCIDENT--WE EITHER DID NOT HEAR/READ BACK A NEW ALT RESTRICTION WHILE 'SWITCHING OUR GEARS' TO A NEW RWY; OR A HDOF/COM PROB EXISTED. THE CONSTANT AIRSPD AND ALT CHANGES ARE COMMON AMONG HIGH DENSITY TCA'S; BUT A RWY CHANGE AT THE LAST MINUTE DIVERTS THE ATTN OF THE COCKPIT; BOTH FROM CLRNCS AND ALSO FROM CLEARING DUTIES (WATCHING FOR OTHER TFC OUTSIDE THE COCKPIT) AT LAX. THIS HAPPENS MUCH TOO OFTEN--ON JUST 1 APCH!