Coming back to the original question, it would be great to see what you find. Since independence, i cannot recollect any significant network changes in big cities that might have fragmented neighbourhoods since a new line is usually laid on empty land skirting existing settlements.
There are other changes like closure of level crossings, new road and foot over/under bridge and gauge conversions that might have a more significant effect to the mobility of people between two sides of a railway line but may not be so visible on historical maps.
It may make sense to focus on one city to study this for ease of use of data collection, and Mumbai might have the best archival records for doing this. This 1931 guide map of Mumbai is very interesting, you can see the location of all the original settlements in the suburbs before the railways brought about their urbanization. It even shows the CST tramway (now CST Road) before the airport was built at Sahar.