Same happened to me just a few weeks ago with JFK-BOS-LHR-CDG, where the JFK-BOS flight saw a similar time change (AA cancelled the prime and BA moved the *BA over).
Quick call to the F/GGL line in Delhi and was moved to JFK-MIA-LHR-CDG, which should give me FFD at JFK and MIA (I'm in F).
Instead of an A321T on JFK-BOS it's a 772 on JFK-MIA (for now).