Do you mean content blocks from other demos of the theme you have installed? This is not possible. You have to have imported the demo in order to have all the content blocks available.
It is not possible either, to use another theme’s content blocks.
What if I want to switch themes back and forth? Is this possible? For example, I install theme #1 and all demo content and then want to switch to theme #2 and do the same. Is this possible?
Yes, it is possible, but it is recommended that you clear database first. Because theme’s are different from one another and the shortcodes of one theme will be junk code to the other theme(will not be recognized) and the site may result in a big mess.
So if you happen to change your mind and want another theme, we strongly recommend to clean database and perform a clean dummy data import from the newly installed theme.
