Complex sentence: Therapists may be trained in one particular method or theoretical orientation, but as they continue to practice they may shift to a more eclectic approach, in which they may add other methods to their original training.
Split into simpler sentences: Therapists may be trained in one particular method or theoretical orientation, but as they continue to practice they may shift their view. One potential shift is from a unilateral approach to using an eclectic, in which they may add other methods to their original training.