Copy test cases to other reequirement

How can I copy existing Test Cases, used in one requirement, to another requirement (so I can then tweak & rename these copied test cases)?

I had a look at "Adding" test cases to the new requirement from the list of Available Test Cases - with a view to adding, copying, editing, and then removing the added test.

This in itself is a not so simple, but also, when I try to do this, the Test Case ID's are not listed in the list of Available Test Cases.

So the question is: Is there an easy way to copy existing test cases to another requirement?

Garrett