Any process that modulates the frequency, rate or extent of cell morphogenesis contributing a phenotypic switch. Cell morphogenesis involved in differentiation is the change in form (cell shape and size) that occurs when relatively unspecialized cells, such as the opaque cells of C. albicans, acquire specialized structural and/or functional features that characterize the cells, tissues, or organs of the mature organism or some other relatively stable phase of the organism's life history.