As a reseller you are able to update the default DNS zone template that is used when creating a new account. Please log in to WHM at http://yourdomain.com/whm
Once you have logged in please go to the "DNS Functions" section of WHM and click on the "Edit Zone Templates" link. Here you will see three templates. The standardvirtualftp template is used when you create a new account through your reseller account. Please choose this template and edit the template with your custom settings.