Yes. Simulated phishing tests are easily paused or cancelled from the Manage Tests page. Campaigns can be paused from the Manage Campaigns page. Data (e.g. actions) will still be collected for paused campaigns/tests; however, any unsent emails will not go out until the test/campaign is unpaused. Ended tests/campaigns will not send out any emails or collect any data. Ended tests/campaigns cannot be restarted.