Its under the security tab in Settings for the feature.
You don't have to do anything to update your plugins. If you have a plugin that does not support re-use on multiple pages you could prevent the is global setting by adding this in the feature definition file:
supportsPageReuse="false"
Features like the Blog and WebStore have this because they use friendly urls that must have the correct page id in the real url that the friendly url maps to so they cannot be used on multiple pages, but it defaults to true if not specified.
Hope that helps,
Joe