Moving the fireworks from 9:45 up to 9:30 is new. On higher crowd days especially, you will not be able to fully experience both. The Fantasmic theater takes a while to exit, and it is a long walk to the front. It is extremely unlikely that you would be able to get close enough to see the projections, which are a big part of the Star Wars show.
You can either:
1) Choose to fully experience one and miss the other;
2) Leave Fantasmic early and try to get a position where you can see the projection screens and fireworks.
If you stay until the end of Fantasmic, you will be able to see some of the fireworks as you walk towards the front, but it is not like Wishes which can be seen from all over the park.
We will be there the same time period. I am really hoping that they announce some second shows for Fantasmic, because the first one always fills to capacity, even on much lower crowd days. If not, I'm going to have some disappointed family members, whichever one we choose.