- Copy the /etc/init.d/tomcat script with a new name in the same directory
- Update the NAME variable in the startup script with a name for the new instance that you want to run.
- Copy /usr/share/$(old)NAME to the (new) NAME you've just created, along with /var/lib/$(old)NAME and /etc/default/$(old)NAME
- Edit the server.xml file under /var/lib/$(new)NAME/conf/ and change all the ports (ie for shutdown, and all your Connectors) so that they don't conflict with the old instance
- Run /etc/init.d/$(new tomcat script name) start
You should now have a running, fully functional instance of Tomcat on the server, using a different port.