Hello,
the changes will take effect when you start generator next time (resuming the process or stasrting from the scratch). Note though that any URLs that were already crawled and added to the crawl queue will still be there, they won't be affected.
If generator is already running, normally there is a link to stop it when you open the Crawling tab. Alternatively, you can manually create empty file via ftp named "interrupt.log" in generator/data/ folder.