Save File Entity file display settings in code - uses CTools exportables.

SaveFileEntityDisplaySettings.php

<?php
  
  // We assume that a custom module is implementing a file formatter
  // called 'mymodule_custom_file_formatter'.

  $filetype = 'video';      // File type to alter file display for.
  $display  = 'preview';    // File display to alter - 'default', 'teaser' or 'preview'.

  $video_display = file_display_new($filetype, $display, 'mymodule_custom_file_formatter');
  $video_display->export_type = 1;
  $video_display->table = 'file_display';
  $video_display->type = 'Normal';
  $video_display->status = 1;
  file_display_save($video_display);