You have, of course, raised one of the most interesting questions currently being debated in our field. Inherent in your question is the understanding that there are a great many therapeutic modalities, all of which have been successful in the hands of their developers, and all of which must be capable of explanation within any successful theory of emotion. By definition, psychopharmacology alters hardware, interpersonal talk therapy alters software, and nothing can change firmware (the group of genetically programed subcortical structures responsible for the subroutines that make up the nine innate affects.) I have suggested that psychopharmacology can operate like the little forest of rods and turnbuckles a building contractor places in the basement of a house to lift it in order to repair its foundation; once the foundation is strong and stable, the temporary support structure may be removed and the house capable of sitting on its now-improved foundation. Good psychopharmacology can allow an individual the freedom to experience true affective neutrality and with it the ability to react to any stimulus with whatever affect would normally be triggered. The development of affect management scripts previously unattainable is thus fostered; after these new psychological structures are in place, the supporting medication can often be removed.
You, of course, up the ante by asking whether interpersonal interaction alone can alter affect management scripts that have become frozen in place by the accretion of biological support from internal homeostasis. All of us who have worked in therapy for many years can present anecdotal evidence that your hypothesis is valid, that some people who are willing to undergo dramatic and intense experiences within the therapeutic encounter can "crack through" barriers held in place by well-oiled neurotransmitter mechanisms and so develop the ability to react vastly differently to old stimuli.
When I lecture on this realm, I take care to present the idea that early in infancy the structures of the brain responsible for our emotional reactions are quite plastic and capable of being "formed" in tune with the ambient emotionality of the nurturant family. I have discussed the concept of inherent vs acquired alterations from normal of the hardware involved, and suggested that it is the acquired disturbances of the biology of affect that respond to intense psychotherapy. One of the most interesting examples of this process was presented by John Fowles in his novel "The Magus," which suggests that if one therapist working an hour per week over the course of a year can produce a certain result, than 50 therapists working en mass at the same time can produce an equal result in one hour. (Don't waste time looking at the movie. It missed the point.) Nevertheless, even though I do believe that the verbal/interpersonal therapies can eventually make a difference in acquired disorders of hardware, I think that at least in our era the patient is better served by therapy that blends such work with the kind of hardware support afforded by medication, especially when the acquisition of pathological alterations in affect mechanisms has been very early in development.
I guess the point is that in our current era, no one therapist is as good as a team that includes practitioners from many disciplines. What do you think?