How would I approach doing a URL redirection that has the following effect:
If users come from an Indian IP address: example.com -> india.example.com
Route53 with location based routing would be the typical way to handle location based things. It won't change request domains, but it will route requests to the nearest region.
To achieve that you want, Route53 can add a header that says where the query is coming from. Based on that you can have a web server do a redirect.
Next option is to subscribe to a geolocation database. Use a PHP script to decide on location based on source IP and forward accordingly.