LOCO change at VZM is a better viable option and probably will take place here only.
1. From VZM-ROU is totally under ECoR territory. Doing a loco change at VZM (ECoR) seems more practical.
2. Changing locos at BZA would be wastage of diesel for the entire stretch from BZA-VSKP. Railways are smarter than that, and then why further burden BZA which is already the most burdened station down south?
3....
more... Look at that slack provided between DVD-VZM. The amount of time given is so high that the train can enter all the way to VSKP, undergo a LR and yet reach VZM with a delay of 10-15 mins. The slack is given so as the train arrives VZM early and the loco change takes place at VZM only.