Long-term transformations in photoluminescence of GaAs single crystals treated with pulsed weak magnetic fields have been obtained. Treatments were performed in the multi-pulse (B = 60 mT, f = 10 Hz, <$Etau~=~1,2> ms, t = 5 min) regime. The defect structure transformations were inferred from the radiative recombination spectra within the range 0,6 to 2,5 pm at 300 and 77 K. A possible mechanism of the observed modifications related with electron-spin transformation is discussed.