I've done a search and understand all the challenges of seat selection on DL-coded AF flights.

I finally got an AF agent to assign my seat CDG-JFK (have to wait until check-in for TXL-CDG). She gave me 40L. Seat 45L shows available on the seat map at delta.com. Even though it's further back, that seems like a better seat to me, since there are only two seats in that section instead of three across. Seatguru has nothing good or bad to say about it. Any thoughts? Is it safe for me to change the seat on delta.com, or do I need to call AF again to have them do it?