How do I automatically assign a node to a term? When an user role changes and becomes "writer", there is a rule that creates a new entity type "taxonomy term" name "user name" and assign it to vocabulary "writers". This works.

Now, the user can create stories. When this user creates stories, this content type should be assigned to term "author name" to vocabulary writers.

It is possible without using PHP, simply adding some actions?
If it was me, I would add a term reference field to user, then when the user becomes "writer" and the related term was created I just added that term to user,

Then using rules, when the user creates a story, I would need to attach term to node, likely I have the term Id attached to user so it could be simply attached to node.

in this way no php code is needed.