Someone more up-to-date may correct me, but I believe that this isn't possible within the authoring tool.

It is a relatively straightforward job to switch things around in the JSON once you've exported a course.

Sometimes a workaround can be to copy the page - which is possible in the authoring tool - and then delete out everything you don't want.

I've been able to do this by opening the authoring tool in 2 browsers and copying from one to the other. 

Open the destination page editor in one browser and the source page editor (with the article you want to copy) in the other.  In the destination, copy any article containing content just so the paste areas appear (the article must contain a component). In the source, copy the article you want to move across. Then paste in the destination where you want it to go.