Sound settings, keyboard settings etc can be controled by Registrations and not Patterns/Styles. Patterns/Styles control only the settings within the style e.g. voices used for chords, bass, tempo and other style parameters.
Under the REGISTRATION menu (UTILITY, Page 2/3), you can set the values (On/Off) that should be altered whenever a registration is changed/called up.
When the Registration button is OFF, changing to new styles should NOT change the settings of the keyboard - only the settings within the style.
You cannot erase BLOCK Registrations( Registerations within the keyboard) but you can replace their content with new information. You can however erase SINGLE Registrations since these reside on HD/FD.
Hope this helps.
PS: When you load a Registeration (Registration LED on) , it brings up it's stored settings. Now when you call up a new style (Registration LED off), the settings of the previous Registration remain (THIS IS CORRECT), however, you have just called up a new style which will have it's own style settings BUT you will remain with the previous Keyboard Settings of the Registeration you just called up. Following your example, YES the background instruments (bass and chords...) should change each time you call up a new style either with/without Registrations, but if you call up a new style without Registrations, the keyboard settings will remain unchanged.