No, it's not possible to copy one project area to another project area in externally managed mode.

An exact copy of the data won't work as intended, because element IDs would all end up pointing to the same project area.

If you truly want two separate project areas with the same models imported, you will need to perform the import process again to a separate project area.

However, if the reason you want to make a copy of the project area is to allow different users to work on different versions, there is another option: you can have different workspaces based off the same project.  First, convert your project into actively managed mode by choosing "Manage Project Properties" in the second menu from the right.  On the left side of the page, choose "Domains" and click "Actively managed with Design Manager."  Then, in the configuration drop down menu at the top, please choose "Create workspace."

Alternatively, if the reason you want to make a copy of the project area is to keep an unmodified version, please choose the "Create snapshot" menu item.