Recently I have checked an option to globally deploy custom Office templates in Office 365. Unfortunatelly there is no such an option but there are two manuall steps:

  • Using SharePoint Online you can deploy templates in a SharePoint list and every time when you create a document inside of the list you can chose one of the templates.
  • Upload the template in OneDrive for Business – each user needs to manually upload the templates

Additional information in the following two articles: – Set a file template for a document or form library – Publish a content type from a content publishing hub