Graphitic polytypes - commensurate stacking variants of graphene layers - exhibit pronounced stacking-dependent properties, including intrinsic polarisation, orbital magnetism, and unconventional superconductivity. Switching between these polytypes in a local, efficient, and reversible manner is a key challenge towards novel multi-ferroic devices. Here, we demonstrate reversible transformation of Bernal tetralayers to rhombohedral crystals down to 30-nanometer-scale dimensions, using only nanonewton-scale lateral shear and sub-femtojoule energies per switching event. Conducting-probe force-microscopy experiments, supported by force-field calculations, reveal edge-nucleated boundary solitons that propagate spontaneously to switch commensurate domains, enabled by ultralow pinning at superlubric incommensurate interfaces and long-range strain relaxations extending tens of nanometres beyond the islands. By engineering cavity geometries, we programme elastic coupling between neighbouring islands and tune switching thresholds and trajectories. This reconfigurable “SlideTronic” control establishes a route to multiferroic and nanoelectronic devices based on elastically coupled stacking states.