THE CREW ON A B757 LNDG RWY 12 AT MIA IS INSTRUCTED TO LAND AND HOLD SHORT OF RWY 9R. APPROX 2-3 MI OUT; THE B757 CREW ADVISES THE TWR THAT THEY ARE UNABLE TO LAND AND HOLD SHORT.

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WE WERE CLRED FOR THE ILS RWY 12 AT MIA ARPT. APCH CTLR REQUESTED WE KEEP OUR SPD UP AS LONG AS POSSIBLE. WHEN WE WERE AT THE FINAL APCH FIX; WE WERE SWITCHED TO TWR FREQ. THE TWR CTLR CLRED US TO LAND ON RWY 12; HOLD SHORT OF RWY 9R. WE WERE AT A FASTER SPD THAN NORMAL; TO FACILITATE APCH'S REQUEST. BY THIS TIME WE WERE INSIDE THE FAF; TRYING TO SLOW AND CONFIGURE THE AIRPLANE FOR LNDG. THE CAPT ASKED TWR HOW MUCH RWY WOULD BE AVAILABLE WITH LAHSO AND GOT NO REPLY. HE STARTED TO LOOK AT THE COMPANY SPECIAL PAGES TO FIND A LAHSO RWY AVAILABLE DISTANCE; BUT HAD A HARD TIME SINCE IT WAS DARK AND HE WEARS GLASSES. I FELT UNCOMFORTABLE GETTING A LAHSO CLRNC SO LATE; WHILE WE WERE VERY BUSY. ALSO; OUR UNION HAS ISSUED MANY SAFETY BULLETINS RECOMMENDING PLTS NOT ACCEPT LAHSO CLRNCS UNTIL MANY ISSUES ARE RESOLVED. I TOLD THE CAPT I DIDN'T WANT TO LAND AND HOLD SHORT OF RWY 9R. HE TOLD TWR 'UNABLE TO LAND AND HOLD SHORT.' TWR REPLIED; CANCEL LNDG CLRNC RWY 12; CLRED TO LAND RWY 9L. WE WERE ABOUT 2-3 MI OUT; AND I COULDN'T SEE RWY 9L. WE DIDN'T HAVE ANY NAVAIDS OR FMS DISPLAY SET FOR RWY 9L; AND I WASN'T SURE WHERE RWY 9L WAS IN RELATION TO RWY 12. I ASKED THE CAPT TO DIAL IN THE RWY 9L LOC FREQ; BUT HE WAS BUSY AND DIDN'T HEAR. DURING ALL THIS CONFUSION; SOMEHOW THE AUTOTHROTTLES WERE DISCONNECTED AND I DIDN'T REALIZE IT; GETTING 10 KIAS SLOW. WE WERE BOTH LOOKING OUTSIDE FOR THE 9L RWY AND PICKED UP THE VASI FOR A NORMAL LNDG. TWR PUT US IN A DANGEROUS SIT. LAHSO IS A BAD IDEA. NEXT TIME I'LL GO AROUND.