Weird, why should Yamaha drop functionality which works with all sheet music apps?
They did not drop the 'old' way, that still works.
They just added a new, much easier way.
Just open the score on tablet, load the registration file on the keyboard and optionally press a registration button.
Then press the link button on the tablet and both are linked.
After that, loading the score on the tablet will load the registration file on the keyboard (and optionally activate the button) and vice versa, loading the registration file on the keyboard and optionally pressing the button will load the score on the tablet
In the sysex communication, the full path of the registration file on the keyboard is contained. So one can now easily switch between registration files in different folders on the keyboard ...