You can edit Preset Voices for the Tyros5 and Genos but not for the S970. The COMMON Parameters in YEM are the equivalent of the Voice Set Parameters, but there is no way to edit even those in YEM.
You don't really need to do that because you can save your User Voices to the USB1 drive. Yes... the Voice Set parameters are limited XG Channel messages, but that's the best we can do.
The way our keyboards work is that when we select a Voice it loads... then the Voice Set parameters load to alter Voice with DSP, Envelope, Filter settings, etc. So when we select a "User Voice" (even if we give it another name) the Preset Voice is loaded... than our custom Voice Set file is loaded to modify the Voice as we wanted according to our custom settings.
Joe H