It is nice that you have a "reply" button for submissions, but it would be very useful if I could cut and paste in the message box...

for those frequent situations when I have many duplicate responses.  Is there a way to do that, which I just have not found?

I believe you are referring to the "Reply" button at the submissions view: https://www.jotform.com/help/269-How-to-View-Form-Submissions, you can customize the data with the tools:

On regards of duplicate submissions, you can prevent them by enable the unique submissions feature in your form: https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form 

Let us know if you need more help.

Thank you for your response, but there is no tool for cut and past in that toolbox.  Frustrating.

Have you tried keyboard shortcuts? 

Copy – Hold CTRL on the left side of your keyboard with your left pinky and press C.

Paste – Hold the same CTRL button and press V.

Let us know if you need more help.

Doh.  Slap my head.  Of course.  Thank you.

Welcome, contact us anytime. :-)