If you want to preliminarily stop the recording process, the only thing you can do is to switch to the Nexuiz Demo Recorder window and click on stop processing. However, if Nexuiz is still open and processing a demo, you have to end it manually of wait for it to end. This means that clicking on stop processing button will simply remove all jobs that haven't been started yet from the internal queue of jobs that would normally be processed (of course they won't be removed from your jobs table).