A version of a portlet I'm working on is already deployed to liferay. Is there any way to get that originally deployed war from a running liferay instance?
This is so I could hot-deploy my version and shortly deploy the old version. The original was deployed by Jenkins. Liferay 6.1 ee, Tomcat 7.
If you mean to get back the old version that you put into Liferay's deploy folder: That one is gone. You should be able to get it back through your source control, jenkins or deployment strategy/backup.
However, if you're using tomcat, you can just zip the directory you find in webapps with your app. That one does not need to go through Liferay's deploy folder again, but can directly be deployed to tomcat (either again or to another tomcat). On other Appservers it depends.
All in all this will be a feature of the appserver, not of Liferay.