AN IFR C182 PLT ENCOUNTERED LIGHT RIME ICING AND DID NOT FORCEFULLY REQUEST AN ALT CHANGE TO EXIT ICING CONDITIONS.

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INCIDENT WHERE TRACE TO LIGHT RIME ICING WAS ENCOUNTERED IN AN ACFT (PLAIN OLD C182) NOT EQUIPPED FOR ICING; IFR FLT PLAN. FORECASTS FOR ICING; BUT NO 'KNOWN' ICING FROM PIREP'S. FILED AND WAS CLRED ON AN UNPUBLISHED PREFERRED RTE FROM BOSTON AREA TO S OF NYC. ROUTING 'REQUIRES' 6000 FT. HAVE USED THIS PROPOSED ROUTING (GDM; ORW; CCC; DPK; JFK DIXIE) NUMEROUS TIMES AND ALWAYS GET 'AS FILED' INSTEAD OF HAVING TO GO AROUND TO ETX OR LHY -- SERIOUS DEVS AROUND JFK. THIS TIME; THERE WAS TRACE LIGHT RIME IN A CLOUD BAND 4000-7000 FT. CLR ABOVE. I REQUESTED; BUT WAS DENIED A CLB TO 8000 FT TO AVOID ICING. CTLRS STATED THAT ALTS OTHER THAN 6000 FT WERE NOT AVAILABLE. SO; WE STUCK IT OUT AT 6000 FT; IN AND OUT OF CLOUDS; PICKING UP SOME RIME. S OF JFK; WE REQUESTED AND RECEIVED 8000 FT AND EVENTUALLY HAD TO GO TO 10000 FT TO BE CLR OF THE ICING CLOUDS. BY THIS TIME; WE HAD ACCUMULATED ABOUT 0.400 INCHES OF RIME ICE WHICH STAYED WITH US UNTIL OUR LNDG. WHILE THE OUTCOME OF THE FLT WAS NEVER IN DOUBT; AND THE PLANE SEEMS CAPABLE OF CARRYING THIS AMOUNT OF RIME WITHOUT SIGNIFICANT DETERIORATING OF PERFORMANCE; MY COURSE OF ACTION SHOULD HAVE REQUESTED AN 'IMMEDIATE CHANGE OF ALT' -- IMPLYING THAT WHILE THERE ISN'T A CURRENT EMER; IT COULD DEVELOP INTO ONE IF AN ALT CHANGE WERE NOT APPROVED. THE CTLRS WERE DEALING WITH THEIR NEEDS; AND I WASN'T INSISTENT ENOUGH TO REQUIRE A CHANGE (FROM ATC) FOR MY NEEDS REGARDING SAFETY OF FLT.