Modifying Responses for Slack Events API Webhooks

Hello, is it possible to modify what's sent back from receiving a webhook? I'm trying connect it with a Slack App, specifically the Events API. and it needs to respond to webhooks in a particular way "We’ll send HTTP POST requests to this URL when events occur. As soon as you enter a URL, we’ll send a request with a challenge parameter, and your endpoint must respond with the challenge value. Learn more."