Do you have the Data Manager program?
https://support.casio.com/en/support/download.php?cid=008&pid=67
I'm not able to use it myself, since I don't have a Casio keyboard. But if you can save an AC7 file from your keyboard to your computer, then you might be able to study it to see if you can figure out what format it's in.
I know that Yamaha style files contain three or more chunks, or data blocks-- the MIDI section that contains the two MIDI chunks (the "MThd" header and the "MTrk" tracks), plus a "CASM" section that contains the settings which tell the keyboard how to play the MIDI data. Yamaha hasn't published any information about what's in the "CASM" section, but dedicated sleuths have discovered what they could, most likely by a laborious and lengthy process of creating a style with specific settings and seeing what the "CASM" section looked like, then changing one of the settings and seeing what changed in the "CASM" section, and repeating that process for each available setting and the various possible values for each setting.
I imagine that Casio's accompaniment files probably contain something similar in addition to the MIDI data. If there is no published information about any such section, you'll need to do some sleuthing to figure it out.