Try asking this question on the forum at psrtutorial.com

There might be a 3rd-party software tool that makes it easier to do what you're asking about on a PC or MAC. Yamaha's styles have a wealth of parameters that allow you to control the behavior of the style. But the on-board tools and workflow are half-baked and not meant for serious editing IMO. No undo, can't easily make step edits on a real-time recording, etc. Korgs are a lot better in this regard.
My $.02,
Ted