Add button to default D7 view
See this drupal.org documentation page called How to add a column with dynamically generated action buttons in a View. hook_views_default_views_alter has essentially nothing to do with this task. Optionally an easier path is like Rules with Views Bulk Operations if you can live with like a checkbox per row, and a dropdown for the operation selection.

The more custom a look, or outside of Drupal's default behavior you deviate. The more work you have to do.