look again in the main Composer Menu, above the Custom Style Copy is Pattern Copy, that's the function for copying presets into composer and composer to composer.

Yes, preset is the factory styles which cannot be changed from the Rhythm Group. However you can copy any preset into the composer, where it can be edited in almost any way, then either saved to SD or floppy or copied to the Custom section for permanent storage.

So Pattern Copy is preset to composer or composer to composer. Custom Style Copy is composer to custom or custom to composer.

So to edit a preset and store it in custom you first copy to composer with the Pattern Copy menu, edit to taste, then secondly copy composer to custom with the Custom Style Copy function. If you think about the different types of memory involved, it makes sense... after a while