The quickest and dirtiest way to do this is to add one line to the insert_posts()
function, just before the $imported++;
line:
}
add_post_meta( $post_id, 'raw_import_data', json_encode( $twitter_raw ) );
// NEW LINE (change 1001 to the image ID):
set_post_thumbnail( $post_id, 1001 );
$imported++;
}
This will obviously disappear if you ever update the plugin. There aren’t any hooks built into the plugin to add your desired functionality, so a more rigorous solution would have to periodically query for posts with, say, the keyring_service
post metadata set, check for any that don’t have the thumbnail set, and then set it to the default.