Hi Derek,
There is to ways to adjust a style (I have SX-970 but even the Korg works in the same way).
1. You can go in mixer and every parameter that you touch (vol, pan effect) will be modified for all parts at the same value; at the end you can co to style creator and save.
2. You can go in Style creator and after call the mixer and what you will modify will be modified only for that part (MainA), here don't touch the keys, you can use start stop to play the part, you can have access to another part pushing the button for Main B for example. 2 times Main A for Fill A. at the end exit from mixer and save.
Hope to help you.
Regards
Mihai