Ion irradiation of semiconductors is a well understood method to tune the carrier concentration in a controlled manner. We show that the ferromagnetism in Ga0.94Mn0.06As films, known to be hole-mediated, can be modified by He ion irradiation. The coercivity can be increased by more than three times. The magnetization, Curie temperature and the saturation field along the out-of-plane hard axis all decrease as the fluence increases. The electrical and structural characterization of the irradiated Ga0.94Mn0.06As layers indicates that the controlled amending of magnetism results from a compensation of holes by generated electrical defects and not from a structural modification.