@ranujain - Correct based on my testing you cant use the original post with AWS to configure mutli disk in that way. To accomplish this you could do it in a few different ways.
Have an automation task that makes the needed api call to add the disks. You should be able to use the resize api call. The documentation for that is located here. https://apidocs.morpheusdata.com/reference/resizeinstance
You could use the reference I provided in the previous post to edit the config phase payload. You can reference this post on how to use this better. Edit Instance Configuration Before Deployment
For the mount points you could still use custom options for mount points but you would pass these to an automation task that would run against the OS resource to make the needed configuration at the OS level.