Rationale: I'm using ansible to configure, thru different steps, PostgreSQL instances and I would like to have every part to append its configuration on the previous one.
Ansible is good for bringing your systems to a known consistent state, so your best bet would be to maintain the list of libraries inside Ansible and then simply apply it. If you really don't know what might be in the database, I would have Ansible read the current value, build the new one if the desired library is not there, and apply the new value.
