How can I copy & paste, or duplicate, an existing project?
Click on "new job" and then select "Copy existing job" at the bottom. Then enter the name of the job you want to copy into the text field.
In addition to copying a job, I sometimes copy parts of the XML file that contains the job configuration. You just paste the copied part into the xml file of the new job and reload the configuration (under manage hudson). This is helpful when you change the original job after you created your copy. However, for your use case the copy is the right thing to do.
When you do new job, you can make the choice to copy it from an existing job. Later alter the settings of the new job.