Is there a word or phrase like "code-switching" that applies to behavior rather than language?
You could use the phrase "switch personas" to describe a person changing their behavior/demeanor to suit their circumstances (and/or achieve an aim).
Bob, a paramedic, gets really riled up when his kids are misbehaving, or when arguing with peers, but when on the job, he instantly switches personas to fit the situation when he needs to keep a patient calm, becoming serene in the blink of an eye.
A "persona," in psychology, is basically one of any number of social "masks" we wear to present ourselves to others in the way that the situation calls for. The definition from Merriam-Webster's online dictionary:
persona 2a: an individual's social facade or front that especially in the analytic psychology of C. G. Jung reflects the role in life the individual is playing
An example of the phrase in use:
Bugs Bunny affords a concrete example of Butler's abstract philosophy of performativity. "Elmer's Candid Camera" reveals gender as anything but candid. The cartoon is metatheatrical, a series of vaudeville schticks, in which Bugs, the master of masculine cool, rapidly switches personas: friend, con artist, sadist, athlete, juggler, victim, pious advocate against cruelty to animals, and enraged object of Elmer's alleged homosexual advances.
Source: David Mamet and American Macho by Arthur Holmberg
The usage example is analyzing the behavior of a fictional character (Bugs Bunny), but it applies equally well to real-life behavior in people--the switching (changing) of personas to play our assigned role in a social situation.
Bob, a paramedic, gets really riled up when his kids are misbehaving, or when arguing with peers, but when on the job, he instantly shifts to calm first responder mode [or shifts gears to fit the situation when he needs to keep a patient calm, becoming serene in the blink of an eye.]
While not a verb, people who do this can be called a Zelig after Woody Allen’s mockumentary of the same name. Defined by Oxford Dictionaries as
Zelig: A person who is able to change their appearance, behaviour, or attitudes, so as to be comfortable in any situation. ‘he has become a veritable Zelig of high technology, burrowing into every information industry nook’