I don't believe that is a supported workflow, I have asked my Survey colleagues if they have any ideas. I would suggest it is likely quickest and Easiest to Save the Project As a New File Name and then delete what you don't need rather than trying to Export and then import what you do need into a New Project.
The VCL Export / Import process is the richest form of data transfer Out / In to a BC-HCE Project and that doesnt support Point Clouds or Images. I dont know of any other Rich Format that could do this kind of transfer that you are asking for - however my Survey Buddies may have a different response - will let you know what I hear baclk
Alan