Hold on.

Changing after flying the outbound only doesn't incur any repricing of the base fare. Eg. you bought a W (cheapest flex) for $1800 last month and now they raised the prices to $2000. If you change your flights after flying outbound, they won't ask you to cough up the extra $200 (after all you've already flown one sector and they can't reprice it fairly).

You will still have to pay the change fee. Ex-India I believe it is about INR 3000 - 5000? But ex-JFK change fees are usually $200-400.

And, you need a seat in the fare bucket originally purchased. If that's not available, you will still need to pay the fare difference, however based on the price at time of purchase (eg. the R fare when you bought you ticket was $2100 and now it's $2300 - they'll price the difference as $2100 (R) - $1800 (W)).

Hope that makes sense. I know someone who faces the same issue with frequent J trips to Italy from India, and having to make a lot of date changes works out very expensive.

ETA: Also, availability is much better on USA POS than India POS, but fares are much higher.