In my career as a Probation and Parole Officer I am of course familiar with the situation you are talking about.
The outcome depends entirely on whether the person concerned has insight. Without a modicum of insight: ("Heh, there is s something wrong with me") there is little you can do.
Most people with an undiagnosed PD coming before the court, usually reach their rock bottom and would say such things as "This is not me", "Something made me do this", "I don't know why I did this".
In other words people with an undiagnosed PD are in denial about their problems and are beyond reach as far as therapy is concerned so long they remain in denial.
But once a person admits they have a psychological problem treatment is not too difficult.
Most people with a PD have been diagnosed to have
hypoglycemia. This can be tested with four hour
Medical Test for Hypoglycemia.
It can also be tested with the
Nutrition Behavior Inventory Test (NBI) , although less accurate as the medical test.
Even if they are found to have a Bipolar Disorder, the
Hypoglycemic Diet can help improve symptoms although it may not "cure" the illness. Bipolar Disorder should always be treated by a psychiatrist.
Nutritional and/or drug therapy should be complemented with some psychotherapy. The kind of
psychotherapy I teach is explained at the web site.