Hi Derek,
You could use Murray Best's 'Yamaha Registration Manager' program for PC to modify all of your registrations in batch mode.
https://psrtutorial.com/util/best.htmlHowever, it would be much simpler to set the split points manually, then lock them from being changed by registrations using Parameter Lock.
I don't know why you think that this would be "a heck of a task" since it is very easy to do!
On Genos, once the split points are set as you want them, press MENU (open MENU 2) > touch Utility > Parameter Lock.
Touch the box next to Split Point to check it and then exit from the display. Your Split points will no longer be changed by registrations that contain split point settings. You don't need to modify any registrations, and you don't have to do anything to effect this each time that you turn on the keyboard.
This setting will remain in place, even through power off cycles, until you change it or carry out a system reset.
Try it to see if is achieves what you want. It is much easier than modifying all your registrations, even using Murray's program.
Regards
Ian