A workaround for you while we wait for this long overdue feature:
I use the Soloist picker in cases like this. That way I generate the instrument I want there first, then go back as needed and make it replace the sections I wasn't happy about. Finally, once the whole thing is more or less up to my liking, I move that finished track over to whichever track it was meant to be on.
I've used this trick for example when I wanted the original 12-8 Piano rhythm to only only play chords (took a while, since it's such a jumble of chords & arpeggio), just to give you some idea of use.
I realise it's rather going about things the long way round, but I just wanted to show you it can be done...sort of wink


Just because you can, doesn't mean you should!
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BBox 2022 Audiophile, Mac Pro Intel, OSX 10.6.8, 800x600 (TV VGA)