Check out the PSR-2000 Tutorials web site and you will find much of this explained in detail there. Look at the lessons on saving registrations. The lesson on OTS also explains what exactly gets saved in a OTS (which is a subset of what gets saved in a registration memory button.)
http://devoted.to/PSR2K

Newly created styles could always be saved to floppy. The default location was USER memory, but if you hit the NEXT button you went to FLOPPY DISK and you could simply save the style there.

If a style is saved in a registration button, the style must exist in the preset area or the user area. You cannot save styles loaded from floppy into a registration button.

You can, however, set your own OTS settings and save that in the style itself and save the style to the floppy disk.