Add hook for main content about wordpress-sparkpost HOT 1 CLOSED

Revisiting the issue, I think it makes sense to remove this hook. It doesn't really add much and it over complicates modifications on the content. If someone wants to modify the name of the content substitution value they can use the wpsp_request_body hook as follows.

add_filter('wpsp_request_body', function($body) {
  $body['substitution_data']['my_new_name'] = $body['substitution_data']['content'];
  unset($body['substitution_data']['content']);
  return $body;
});

from wordpress-sparkpost.