My current version 0.04 is available here: http://22.214.171.124/perl/
To implement a method to change the default value of an already existing field you would need to change the text in more than one place in the PDF structure. First place to change would be the DV value of an Annotation object. This would do it for Acrobat Reader unless the PDF is damaged, but Foxit Reader would still show the old Default Value. This is because an editable field is presentated in two different objects. One that is the actually field, and one that is formatted just like all other text in the document. So the idea is probably that if the reader is too old to show the editable field, it will at least show the Default Value as text.