Would be a great feature addition if you could apply a task template in a project to an already created task. Notion has this feature for tasks that have already been created - you just delete all the content in the body of the database item and it allows you to apply a template to that task. To my knowledge, this isn’t possible in Asana. Please correct me if I’m wrong.
I know Asana has a way to merge duplicate tasks together (for instance, if someone created a task and someone else created a task with the template, you can merge those two together into one), but it’s not quite the same.