I think what I'm gonna do is build an arranger that just redistributes the style notes onto new chordals from "as recorded in style" quality to "as wanted by PLAYED chord" quality in as plain a manner as possible - just pick the next dang chordal up valid in played chord. And see how it sounds. It won't be an identical arrangement to yamaha's. But it'll still sound good per chord quality.

If a style composer happens by later and can fill me in, I'll change my algorithm.

In addition to the weird yamaha "pick next chordal" thing, there are also cases where ONE (or some) of a style's note(s) are duplicated. Not just shifting the chordal, but making a whole new one.

Here's an example:
style channel was plain CMaj7 chord quality with 3g,4b,4e notes

when major chord is played, out come 3g,4c,4e as you'ld expect. As 7 is often hopped to 1

BUT when C79 is played, out comes 3Bb,4c,4e,4d

Where the heck did that extra note come from??? The style only had 3 notes...