ContentObj in html emails


I’m trying to write a scrip similar to Edit mail content before Notification

I use
to obtain content and
$self->TransactionObj->ContentObj->__Set( Field => ‘Content’, Value => $content)
to set content.

The problem is, in a multipart email where the first part is text/plain and the second is text/html, the scrip modifies text/plain part, whereas RT displays and sends to recipients the text/html part.

Is there a way to modify either the part, which RT considers to be the “main” part of the message, or both text/plain and text/html parts?