You can customize the behaviour of all Scrapy components -- including the core, extensions, pipelines and spiders themselves -- via Scrapy settings. These settings are usually defined in your Scrapy project's settings.py file, but you can also manage them through Scrapy Cloud's web interface.
First go to your project Dashboard and and then go to the Spiders Settings page. There you can add or remove the Scrapy settings using the (+) or (x) buttons, as shown below:
Then you can customize your settings, click "Save" and that's it!
For a list of available built-in settings see: Built-in settings reference.