Is it possible to change or assign new parent to the Model instance that already in datastore? For example I need something like this

task = db.get(db.Key(task_key))
project = db.get(db.Key(project_key))
task.parent = project
task.put()

but it doesn't works this way because task.parent is built-in method. I was thinking about creating a new Key instance for the task but there is no way to change key as well.

Any thoughts?