This feature seems to be used internally by Octopus Deploy and can be seen in the "Deploy an IIS Web Site" step template created by Octopus Deploy.

When I add the "Deploy an IIS Web Site" step template created by Octopus Deploy to a project process I am presented with 3 options under the "IIS Deployment Type". As I select the different radio buttons the actual step template parameters that the user is able to fill out changes.

For example, when I switch from the "IIS Web Site" option to the "IIS Web Application" option, the very next section changes from "IIS Web Site" to "IIS Web Application" and the fields the user is expected to fill out changes between the two as well.

To be clear, what I'm trying to achieve here is as follows:

I want to create a step template similar to Octopus.IIS where the user can select one of a few options at the top of the template. Based on their selection I want the required parameters the user is expected to fill out for the step template to change.