We present a theoretical model of magnetorheological effects in a soft magnetic gel with non spherical (disc-shaped) magnetizable particles. This model is based on micro-mechanic consideration of the particles reorientation in a soft elastic-viscous medium after step-wise alternation of an applied magnetic field. Analysis of dynamics of the composite macroscopic shear modulus change after the field alternation is in focus of our consideration. The presented results explain recently experimentally observed magnetorheological and relaxation effects in ferrogels with the discotic particles: increase of the composite modulus under the field action; relaxation of its storage and loss components as well as overshoot of the loss modulus after the field stepwise activation and deactivation.