Not a big deal buddy. It has been done on Jammu Tawi - Katra line of NR and CR also did DC - AC conversion on its route. It was almost like laying new OHEs replacing the old ones on Thull and Bhor ghats. KR as a subsidairy of IR is a pioneer in technology. When it can lay a railway line on one of the toughest terrains in India then electrifying tunnels won't be a major hurdle for them.