Actually i think as far as i have noticed.....Even if the Loco change is shifted to MMR , still 12780 will have to halt for 10 minutes. So 10 minutes BSL and then 25 minutes at MMR , so extra time will be needed to added in TT (Plus the slack between MMR-KPG would needed to be reduced if average speed end to end required is SF class) , so saving some time the loco change plus crew change is also done at BSL itself.
Or else 1st Crew would be needed to be changed at BSL and then further Loco separately at MMR which can be Tedious.