Update an existing email template. This is the v3 equivalent of the v1 message_template_edit action.

Requires the UpdateEmailTemplates permission and access to the template being updated, otherwise the request answers 403; an unknown id answers 404.

The content of the template can also be reseeded from an existing campaign or template instead of being supplied directly: send basecampaignid to copy the content of a campaign message, or basetemplateid to copy the content of another template (a numeric id, which requires access to that template) or of a stock template (its identifier). The design of the source is carried over with the markup.