The example below will allow you to add a hidden field to your form while customizing the field name and field value.

Change 554, 555, and 556 to the IDs of the fields that you want to make conditionally read-only.

When you integrate with other plugins, some may expect a format other that the standard yyyy-mm-dd the Formidable uses. In this case, you can add a hidden field to your form, and use custom code to fill it with the date in the format you need.