Currently there is only one way to programmatically add a task to a project: https://developers.whmcs.com/api-reference/addprojecttask/
It would be very useful to have a new endpoint like: assign-task-template to make the process of adding projects with a predefined lists of tasks much easier with less duplicatin when using API
You could define the task template in the admin GUI
Take all the same params as "addprojecttask" except change the task title to task template title
This would add all the tasks from within that template to the project without having to add them individually via the addprojecttask command.
For certain projects, the tasks are repeatable at scale. Hence why templates are there. To add projects using hooks and the API is very useful, but its only half working if you cannot utilize already existing templates. Otherwise you need to manually assign these tasks.
If you update the task template, you will need to remember to update the API calls to factor in new tasks too. You are basically doubling up on the workload.