CARJ FLT CREW HAS TRACK DEV AT IAH WHEN THEY FAIL TO REPROGRAM LATE RWY/ILS CHANGE IN THE FMS.

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WHILE ON THE STROS 4 ARR; I BRIEFED THE ILS RWY 26L APCH IN ANTICIPATION OF BEING ASSIGNED THAT RWY FOR LNDG. WE (MY FO AND I) HAD DECIDED TO ENTER AN APCH IN THE FMS PRIOR TO BEING TOLD TO EXPECT ANY PARTICULAR RWY; SO THAT THE FMS WOULD DISPLAY ALL THE FIXES ON THE ARR. HAD WE NOT ENTERED A RWY; SEVERAL OF THE ARR FIXES WOULD HAVE BEEN MISSING FROM OUR MFD. AFTER BRIEFING THE ILS RWY 26L; HOWEVER; WE WERE TOLD TO EXPECT THE ILS RWY 27. WE THEN ENTERED THE NEW ILS FREQ (110.9) AND I BRIEFED THE NEW APCH. WE WERE GIVEN A VECTOR FROM STROS; TO JOIN THE LOC RWY 27. SINCE WE WERE APPROX 22 NM FROM THE RWY (BEYOND THE LOC SVC LIMIT); I DECIDED TO REMAIN IN WHITE NEEDLES (FMS DATA) UNTIL CLOSER TO THE ARPT; AT WHICH POINT I PLANNED TO SWITCH TO GREEN NEEDLES (ILS DATA). AS WE GOT CLOSER TO THE COURSE LINE ON MY MFD; I REALIZED THAT I WASN'T GETTING THE BLUE LOC NAV NEEDLES THAT USUALLY APPEAR WHILE NAVING IN WHITE NEEDLES WITH A LOC FREQ TUNED. I LOOKED OVER AT THE FO'S MFD AND REALIZED THAT HE WAS RECEIVING A COURSE INDICATION FROM HIS ILS NEEDLES. JUST THEN TWR INFORMED US THAT WE APPEARED TO BE PASSING THROUGH OUR COURSE AND GAVE US A VECTOR TO REJOIN. THEY ALSO ASKED US IF WE HAD 110.9 TUNED IN; WHICH WE VERIFIED. THEN THEY SAID WE DIDN'T APPEAR TO BE JOINING THE COURSE AND GAVE US A 180 DEG HDG TO DEPART THE APCH COURSE. AT THAT MOMENT WE BOTH DECIDED TO CHK THE FMS; AND DISCOVERED THAT WE STILL HAD ILS 26L PROGRAMMED. THE FO THEN ENTERED ILS RWY 27 IN THE FMS AND WE WERE REVECTORED TO JOIN THE APCH. WE SUCCESSFULLY INTERCEPTED THE ILS AND LANDED ON RWY 27. I THINK I SHOULD HAVE REQUESTED THAT WE BE RE-VECTORED WHEN I NOTICED THAT I WASN'T RECEIVING ILS NEEDLE PRESENTATION; WHILE BEING VECTORED TO JOIN THE APCH. I THINK PREVIOUS EXPERIENCES OF BEING TOLD TO JOIN AN APCH WHILE STILL BEYOND THE NORMAL ILS SVC LIMIT; FOLLOWED BY ERRONEOUS ILS NEEDLE INDICATIONS; CAUSED ME TO SECOND-GUESS RELYING SOLELY ON THE LOC FOR RWY 27 WHILE STILL BEYOND THE NORMAL SVC LIMIT. IN THE FUTURE I WILL VERIFY THE APCH ENTERED IN THE FMS IN ADDITION TO THE LOC FREQ SO THAT I MAY SERVE AS A BACK UP WHEN GIVEN A VECTOR TO JOIN A LOC COURSE.