A short explanation to create different patterns depending on the chords played is at http://www.jososoft.dk/yamaha/articles/style_11.htm
Link to releavant software at that page too.
I have no software to edit individual notes. Can be done in sequencer software as style files are MIDI files with some aditional data interleaved.
Before editing preserve this non-MIDI data by using my "Style Split and Splice" software at http://www.jososoft.dk/yamaha/software/sands/index.htm
------------------ The Unofficial YAMAHA Keyboard Resource Site