Custom Styles is a Technics jargon term for style files prepared and made available in a particular format that end up in the Custom style button area in the rhythm group of buttons.
custom-made styles for particular songs is a different thing altogether and is the usual meaning of the phrase custom-made which means made specifically to enable the performance of a particular song. Files of this nature when loaded either from SD Card or floppy disk will almost certainly end up being found when you depress the Memory Load button in the Rhythm Group of buttons.
Hoped all this helps, Bernie...
Rog