Adding default and hidden values to metadata using UI SDK

Hi

Is there a way of adding a default value to a xmp_property though using the UI SDK?

Also is there a way using the UI SDK of adding metada to a document without it appearing on the panel view?

For example I want to add to a file an XMP label "animal" with the value "cat" by using the UI SDK but without the info being displayed on the panel.

Thanks

Trevor