I hear ya...
FYI...yesterday I experimented with the process to re-record a section on a song. (Worked great by the way). I copied the song into a folder called Testing. So I could screw anything up, even if just for fun
So, on that one it asks for a name, so it prompts you to be able to save it with a different name. So that seems relatively safe. But the fallback I will use, at least a short term safety net, is copy original to a different folder and attempt the changes.
I expect that changes with the mixer will work the same. I will report back. I expect to play with the mixer today.
I'll just reiterate...the documentation is fair at best.
This keyboard is SO different in doing the same things as the 660. Last night after my test with updating a couple measures, I wanted to play the song, as an accompaniment (ACMP), I struggled with how to change the volume of the live part of the song. (One of my goals is to have ACMPsI created to play in the background of the melody which I would play live). I would use a different instrument than the main one recorded in the ACMP and it would change the instrument I was trying to play live to the main instrument in the ACMP. Then figuring out how to change the volume of the live instrument was a pain.
I'll get it figured out eventually.