Since statistically isotropic fractal aggregates of particles are a particular case of self-organized critical systems, we describe formally field-induced behaviors of aggregated ferrofluids as responses of regular at-equilibrium critical systems at the critical point to the small field conjugated to its order parameter. This leads us to expect some general scaling laws, which are checked numerically on two examples: the magnetic susceptibility and the magneto-optical linear dichroism of two-dimensional aggregated ferrofluids. This is performed by numerical simulations of such an aggregating system under weak magnetic field applied in the plane of the aggregates.