Whetever method everyone uses to make a new style it is very time consuming.
That's what I see
That is why I prefer the assembly function and changing an existing style little by little,section by section on the keyboard to fit to a specific song.
Is the result the best it could be done?
Maybe not but when I done I have repeated the song's patterns so many times that I have learned to play it.
That it was my goal from the very beginning anyway.
To learn a specific song/melody and find a nice arrangement that fits with it's sections and patterns.
If you cannot find easily a pattern for a part that you want,
you can still record someting by yourself,or insert part/parts from a midi file,
where someone else has allready done the job for you and he spent
his time to imitate/copy a song to a midi format.
I am not a style maker or anything just saying my opinion.