There are two types of channel for each part in a style file-- the source channel and the destination channel.
You can have a part-- such as Rhythm 1-- that is coded on channel 7 within the MIDI portion of the style file, which would be indicated for that part by specifying a source channel of 7 in the CASM chunk (so the keyboard knows it's supposed to get the data for that part by reading channel 7 from the MIDI portion), but then you can specify that the part is to have a destination channel of 9 (so the keyboard knows it's supposed to use that data for the Rhythm 1 part).
You can even have multiple source channels that are mapped to the same destination channel, allowing you to have alternate versions of the part depending on which types of chords are being used, by making use of the CASM fields that specify which types of chords are valid for each of those source channels for that part.
Note: All channel numbers given above are according to the "humanized" 1-through-16 numbering, rather than according to the 0-through-15 numbering that's actually used within the MIDI data.