Hi there! I wonder if whether criminal behavior is modifiable through social work services and, if so, what theory may facilitate or guide best achieve change among correctional clients.

My pleasure.

Thank you for letting me know!

Great question! Despite what we often say: a leopard can't change its spots, there is a broad consensus in the social-psychological literature that attitudes play a significant role in behavior. The theory of reasoned action (Ajzen & Fishbein, 1980) is one of the best-known models of the attitude-behavior relationship and illustrates the complexity between cognition and action. Accordingly, there is a sequence of events that begins with certain attitudes about a behavior (“attitude toward the behavior”), which are then evaluated against perceived social reactions (“subjective norm”), which give rise to the formation of self-instructions whether to engage in a certain act (“intention”). Research spanning a wide spectrum of attitude-behavior relationships has found support for this model, with intention playing a particularly strong role.

You may read more through the below reference:
Ajzen, I., & Fishbein, M. (1980). Understanding attitude and predicting behavior. Englewood Cliffs, NJ: Prentice Hall.