Limited naval impact if Sweden joined the Axis

How would the naval war change if Sweden joined the Axis?

Not greatly at sea, because Sweden could not seriously challenge the Royal Navy, but the postwar Scandinavian settlement could change substantially.

Sweden lacked enough deployable naval strength to cause the Royal Navy major trouble. Britain might decide that attacking the Swedish ships was not worth the cost. The more consequential effects would come later, as Norway or the Soviet Union used Sweden's belligerence to revisit territory and influence in Scandinavia. The immediate naval threat would be limited even if the postwar political consequences were substantial.