FLT CREW DEPARTED IN WRONG ACR MLG THAN DESIGNATED ON FLT RELEASE.

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ACFT HAD MEL 74-1 HIGH ENERGY IGN SYS LEFT IGNITOR INOP. LEFT MAY BE INOP PER MEL. FLT ORIGINATED DET-STL. THE DISPATCH HAD PLANNED A PLANE SWAP IN STL; BUT STATION HAD NOT GOTTEN THE WORD. TRW AND RS WERE FORECAST FOR PHX WHICH WAS NEXT STOP. THERE IS A SVC BULLETIN #T88-13-51 IN AFFECT IN REF TO AIRLINES IN NEW ORLEANS THAT REQUIRES BOTH HIGH IGN SYS TO BE OPERATIONAL WHEN DISPATCHED INTO KNOWN OR FORECAST MODERATE PRECIPITATION. BULLETIN T-88-13-51 IS NOT INCORPORATED INTO MEL; SO I ASSUMED I WAS LEGAL TO OPERATE ACFT UNDER MEL 74-1 OR RIGHT IGNITOR. STL STATION LOADED ACFT AND DISPATCHED. I SIGNED DISPATCH RELEASE AND NOTICED EXCESS LOAD OF FUEL AND A LNDG ALTERNATE FOR PHX OF LAS. RECHKING THE CURRENT WX AND FORECAST SHOWED 1) TRW AND RS - FORECAST TO CLR. WHAT I DID NOT NOTICE WAS A DIFFERENT ACFT # ON RELEASE AND STL STATION WAS UNAWARE OF PLANNED ACFT SWAP. WE DEPARTED UNEVENTFUL AND WERE APPROX 10000' TO 11000' WHEN DISPATCH PHONE PATCHED US TO STANDBY FOR POSSIBLE RETURN TO STL. THEY DETERMINED THE SVC BULLETIN T-88-13-51 WAS STILL IN EFFECT AND WE WOULD BE IN VIOLATION OF SUCH IF WE PROCEEDED TO PHX. WE RETURNED TO STL; SWAPPED ACFT AND PROCEEDED WITH A NORMAL FLT TO PHX WHERE WE ENCOUNTERED NO PRECIPITATION ENRTE OR ON ARR. MY INITIAL CONCERN WAS FOR BEING VIOLATED FOR SIGNING FOR THE WRONG ACFT. I AM NOW MORE CONCERNED WITH BULLETINS THAT ARE NOT INCORPORATED INTO THE MEL LIST. JUST A NOTE TO THE EFFECT THAT THE CREW NEEDS TO TAKE REF TO THE BULLETIN OR WX BRIEF WOULD HAVE MADE ME MORE AWARE OF WHAT LIMITATION HAD BEEN PLACED ON ME. ALSO; IT TURNED OUT THAT THE STL STATION CETA MACHINE WAS INOP AT THE TIME OF ARR OF FLT; SO THEY HAD NOT KNOWN OF AIRPLANE SWAP AND DISPATCH HAD NOT VERIFIED WITH A PHONE CALL.