Dr. George Simon begins:

In a sense, the question of whether a disturbed character can change is without much meaning. The simple answer to that question is: yes, manipulators, and any disturbed character for that matter, being human beings with free will, can (i.e. have the power to) change. But the more crucial and meaningful questions are: Under what circumstances are they likely to be motivated to change? Does changing their outward behavior mean they’ve really had a change of heart? and, How do you know whether a change you think you see will be genuine and lasting? http://counsellingresource.com/featu...n-they-change/

His thesis follows before concluding:

While they might take some heart in the notion that people can and do change, they need to remember that change is always the responsibility of the person with the character deficiency. Sometimes professional help is necessary. But the motivation for any change has to come from that person, arising out of their sincere desire to grow and mature in character. It’s important to find a helping professional who not only understands and appreciates this but also knows how to really aid in the process. And it’s equally important to enter the process only when the right motivation is present. Most of the time, the motivation arises only when circumstances have forced the issue (i.e. the person has lost too much, or the costs of their behavior have risen too high).

Bottom line: There’s always room for hope, but it’s absolutely essential to hold a person accountable, not only for outward behavior changes, but for the consistent and pervasive behavioral evidence that their heart and mind are changing as well.

If what we are doing is not working, changes are necessary. Simon's discourse on how to change provides some guidance. Others have different ideas. In any event, Simon gives us something to think about.