Thanks for your post Kendall,

I am afraid that you can not copy and paste diagrams from one JUDE project to another like you noticed.

The only way to do now is to merge two projects.
Select [File] - [Merge Projects] from Main Menu.

A 20-day free evaluation license for JUDE/Professional is available from here.
(Merge option is supported only in JUDE/Professional)
http://jude.change-vision.com/jude-web/getEvaluationLicenseButton.do

We will sincerely consider making the copy and paste possible over JUDE files in future release.

Thank you.
-Satomi