I would like to add a sidebar to all post pages. When i created post pages I chose the layout content/sidebar. Now I would like to have sidebar/content/sidebar. Changing it in Customize/sidebar layout, did not have any effect on already published post pages.
If you’ve manually changed those settings inside the post, then yes.
The sidebar settings inside the post are meant for pages/posts that need a different layout than the global setting in the Customizer, which is why the default is “Global Layout Setting”.