3 points
to change the backings with chord changes you can copy to composer and use the chord modify change. Some experimentation may be needed but it works very well, and is programmable for each track and each note of composer and pads.
for fills for easy composer creations I just copy individual fills from any suitable style into the appropriate slots, you have 8 fills to choose from each preset. You can still edit them once copied, add tracks/notes, delete tracks/notes, change voices etc etc.
for band in a box, just make a midi file of the style, intro, a, b, fill, ending etc in C major. Then load the midi as nx and do a sequencer to composer copy for the (1-4)intro measures, the (5-8)a measures, the (9-12)b measures etc etc for example into the appropriate composer slot. Assign voices, balance etc.