LATE RWY CHANGE AND FMC REPROGRAMMING CARRIED OUT BY PLT FLYING RESULTS IN A TRACK DEVIATION.

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UPON ARR INTO ATL; ON A LEG IN WHICH I (THE FO) WAS THE PF; WE BEGAN THE HONIE 5 ARR VIA THE SZW TRANSITION. I HAD BRIEFED AND PROGRAMMED THE HONIE ARR WITH AN ILS TO A VISUAL APCH; RWY 28. AT ABOUT HONIE INTXN WE WERE ASSIGNED RWY 27L. I BEGAN BY GOING TO HDG MODE TO ALLOW ME TO PERFORM THE FMS REPROGRAMMING. I COMPLETED THE REPROGRAMMING OF THE FMS AT APPROX TIROE INTXN. JUST AS I BEGAN TO REENGAGE THE LNAV FUNCTION WE PASSED OVER TIROE. THE LNAV PERCEIVED TIROE BEHIND US AND BEGAN A 180 DEG TURN. I CAUGHT THIS ERROR AND RE-ENGAGED HDG SELECT REPROGRAMMED FOR FOGOG AND BELIEVED I HAD AVERTED A PROBLEM. I HAD NOT HOWEVER; RE-ENGAGED LNAV (AGAIN). THIS CAUSED US TO FLY PAST THE TURN AT FOGOG IN HDG SELECT. ATC NOTIFIED US. THE PRIMARY CAUSE OF THIS INCIDENT WAS MY INABILITY TO COORDINATE AUTOPLT USAGE WITH MY FMS PROGRAMMING. (ALWAYS HAVE ONE MORE BUTTON TO PUSH.) SECONDARY FACTORS: 1) THE LATE RWY ASSIGNMENT FROM ATL AND LACK OF FLT CREW'S ABILITY TO GUESS WHICH RWY (WITH BETTER THAN 50% ACCURACY). 2) SIGNIFICANT FREQ CONGESTION DOES NOT ALLOW FOR DELEGATING PNF TO REPROGRAM FOR PF. 3) HIGH COCKPIT WORKLOAD -- BAD TIME TO HAVE TO REPROGRAM AND REBRIEF FOR APCH AND ARR.