If you are a purist, you should install the base MSTS from your original CD, then use a "Pre-installed Add-on Installer" that simply copies the India-specific assets into your clean install.

Microsoft Train Simulator is a train simulation game developed by Microsoft and released in 2001. The game allows players to drive various trains on different routes, with realistic controls and scenery. MSTS has a dedicated community of fans who create custom content, including new trains, routes, and scenarios, using the game's built-in tools and APIs.

for modern simulators including MSTS and Train Simulator Classic. Why Railfans Prefer Them Zero Configuration

: Because MSTS was notoriously difficult to mod (requiring specific folder structures and registry tweaks), "pre-installed" versions became the gold standard. These were often shared via USB drives in college hostels or sold as "Add-on Packs" in local computer markets. The Content : These packs typically included: