In all probability, they are replacing a loco due for POH with a fresh one. 12625 TVC - NDLS Kerala Express too has a loco change @ ED, from WAP 4 to WAP 4; it gets a fresh loco which will go NDLS & bring the train back to ERS as 12626.
Its not a due for POH one , they are terminating the loco link at ED , Most of the locos will go to shed after a long haul . POH is done for loco for once in 8 years or 9 years which takes a month for completion. This change is just to terminate the link and provide a new loco for further journey as Erode does not have much of a terminating trains.
Disclaimer: This website has NO affiliation with the Government-run site of Indian Railways. This site does NOT claim 100% accuracy of fast-changing Rail Information. YOU are responsible for independently confirming the validity of information through other sources.