ALTDEV; ALT EXCURSION IN PREMATURE DSCNT RESULTING IN A POSSIBLE XING RESTRICTION VIOLATION.

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NEW YORK CLRED THE FLT TO CROSS CCC AT AND MAINTAIN 5000 FT THEN CLRED THE FLT FOR THE ILS RWY 24 APCH TO ISLIP LONG ISLAND ARPT. I STARTED TO DSND TO THE INITIAL APCH ALT OF 2000 AS I WAS 'CLRED FOR THE APCH.' MY UNDERSTANDING BEING THAT THIS SUPERSEDED THE 5000 FT XING ALT. AT 4600 FT MSL; THE CAPT; WHO WAS TALKING ON COMPANY FREQ; CALLED MY ATTN TO THE XING RESTRICTION. I RETURNED TO 5000 FT. NEW YORK ASKED FOR ACFT ALT. WE ANSWERED WITH 5000 FT AS THE ACFT WAS NOW BACK ON ALT. TOTAL TIME OF INCIDENT: 30 SECONDS. MY ORIGINAL QUESTION ADDRESSED TO THE CAPT WAS; 'DO WE STILL HAVE TO CROSS CCC AT 5000 FT?' HE WAS TALKING TO FLT CTL AND DID NOT ANSWER. I UNDERSTOOD THE þCLRED FOR APCHþ TO SUPERSEDE THE XING RESTRICTION. ON REVIEW OF THE APCH PLATE; THE OUTBOUND COURSE OF 271 DEGS AT 2000 FT WAS THE REASON I BEGAN THE DSCNT. THIS WAS THE CAUSE OF THE AMBIGUITY. DID THE 'CLRED FOR THE APCH' WHICH WAS GIVEN DURING A SECOND XMISSION FROM ATC; RELEASE ME OF THE XING RESTRICTION? ATC'S REQUEST FOR ALT VERIFICATION; MAKES ME WONDER ABOUT IT!