Hi Mick,
Normally one works either with OTS or with registrations. If, for whatever reason, you are also using OTS while playing with registrations, you should definitely switch the OTS LINK function OFF.
You can save all changes to the style and the keyboard voice settings directly in registrations. HOW you make the keyboard voice settings, e.g. using the OTS of the currently loaded style or selecting the keyboard voices manually) does not matter. The current status of the keyboard is always saved in registrations (of course also depending on which parameter groups are ticked in the Memory window).
If for any reason you want to change the OTS of the current style (Memory button > desired OTS button), as Eileen mentioned, you need to resave the style file. But usually this is not necessary if you work with registrations anyway.
Best regards,
Chris