NON ADHERENCE TO ATC CLRNC INSTRUCTION LEADS TO AN ALTDEV ALT EXCURSION.

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ON MY WAY BACK FROM MOLOKAI; I WAS CLRED INTO THE HNL TCA. I WAS TOLD TO MAINTAIN 2000 FT MSL AND APCH OVER THE FREEWAY; HDG W TO HNL. THE APCH CTLR THEN HANDED ME OFF TO TWR. I CONTACTED THE TWR AND WAS TOLD TO RPT ENTERING A DOWNWIND TO RWY 4L. I LISTENED ON THE FREQ AND HEARD NO OTHER TFC COMING MY WAY. HNL ARPT ELEVATION IS 13 FT; AND NEVER HEARING AN ALT RESTRICTION OF 2000 FT; I STARTED TO DSND TO TFC PATTERN ALT OF 800 FT MSL. AS I WAS PASSING 1700 FT MSL; THE HNL TWR CTLR CALLED ME AND SAID 'HNL ALTIMETER 30.02.' I GAVE MY CALL SIGN BACK THAT WE AGREED. AS I WAS PASSING THROUGH 1500 FT MSL; THE TWR CALLED AND SAID; IS THAT YOU DSNDING ON YOUR OWN?' I REPLIED; 'THAT'S AFFIRMATIVE.' THE TWR THEN TOLD ME 'CLRED TO LAND 4L.' I LANDED 4L. I DID NOT BELIEVE I HAD AN ALT RESTRICTION ON ME. THE ONLY REASON I REALIZED SOMETHING WAS WRONG WAS WHEN THE MAN FLYING WITH ME (THOUSANDS-HRS PLT) TOLD ME WHEN THE CTLR CALLS YOU AND GIVES YOU THE ALTIMETER SETTING; IT'S LIKE A WARNING TO YOU. WELL; WHY BE COY -- TELL ME NOW WHAT'S WRONG SO I CAN FIX IT! I WAS EXTREMELY DISTURBED ABOUT HOW THIS HAPPENED BECAUSE I CONSIDER MYSELF VERY DILIGENT IN MY EFFORTS TO BE SAFE AND ADHERE TO REG. WHAT IS MORE FRUSTRATING IS; THIS HAPPENED ON THE SAME DAY THE TWR CLRED US TO TKOF ON 4L WHEN ANOTHER PLANE WAS LNDG -- NOT A GOOD DAY!