I think you have misunderstood. What I plan to do is change NRT-BKK to KIX-BKK because my flight into NRT will be changed to land in HND and not NRT. It might be possible to get from HND to NRT to make the original flight, but it would probably be cutting it close, and I would rather not stress out about making the only connection of the day to BKK on JL. I need to get to BKK on the originally planned day because I have a lot of other travel that would need to be re-booked if I don't.

I will keep your experience with duplicate bookings in mind before I decide what to do.