This is sometimes called "faceted".
Some people, while not technically multiples, still display some of the characteristics in the form of "aspecting." These people exhibit distinct outward personality shifts, perspective shifts, etc. without experiencing a difference in memory retention, a sense of being a different person, or a loss of self-perspective.
Thus someone can have different ways to act in different situations without technically being a separate person. [However, if shifts include memory difficulties, or feelings of not being in control of your actions when you're doing something (a feeling that you're watching or feeling your body doing things YOU are not controlling) then this probably isn't the answer to the shifts in your personality.]
"Past Life aspecting" - someone who defines aspects along lines of separate lives (ie: "aspecting along past life lines" or "past-life aspect")
"Form aspecting" - someone who defines aspects along lines of separate physical forms/races