>Yes, you can customize the WAF challenge or WAF block page. It is included in the Custom Error page editor.
The difference between the challenge and block page is that on the challenge page, a CAPTCHA is presented. If the user successfully enters the CAPTCHA, the action continues. On a block page, there is no CAPTCHA so the action has no way to proceed. You can choose from the Web Application Firewall interface whether you want an action to be challenged or blocked.