FYI you can accomplish exactly this with my Flowsana integration. It has an If-Then Rule action of “add subtasks from a template”. If you want the same set of subtasks added for every form submission in the project, you can trigger that rule action with “If a new task is added” which will fire whenever a new form is submitted. Or for added flexibility, you could even have a different set of subtasks be added depending on a form field that you map to a custom field.
The above solution handles this as well - the template task containing the subtasks can reside in any project you choose. So you could restrict access to that project to only those users who you want to be able to edit the subtask template(s).