We learned in Chiang Mai that only the big boss has authority to sign the Thai marriage document for a farang+thai marriage. As we want to have the same marriage date as our wedding ceremony date, we've been able to book in advance the big boss to make a quick stop at the ceremony to issue the paperwork+signatures, etc..
The venue's wedding planner who has worked with many weddings, said their might be an extra "fee" for this official to come, also considering it's a Saturday, 3-day weekend, 1 hour drive in the mountains away from the Amphur Office. She mentioned years ago in Mae