A dynamic covalent library of interconverting imine constituents, dissolved in an acetonitrile/water mixture, undergoes constitutional reorganization upon phase separation induced by a physical stimulus (heat) or a chemical effector (inorganic salt, carbohydrate, organic solvent). The process has been made reversible, regenerating the initial library upon phase reunification. It represents the behavior of a dynamic covalent library upon reversible phase separation and its adaptation to a phase change, with up-regulation in each phase of-the fittest constituents by component selection. Finally, the system exemplifies the splitting of a 2D (square) constitutional dynamic network into a 3D (cube) one.