We demonstrate controlled excitation of Bloch modes and manipulation of diffraction and refraction in optically induced two-dimensional photonic lattices. Solely by adjusting the bias condition, the lattice structures can be reconfigured at ease, enabling the observation of transition between Bloch modes associated with different high-symmetry points of a photonic band, and interplay between normal and anomalous diffraction as well as positive and negative refraction under identical excitation condition.