We investigate the role of carriers in the presence of oxygen vacancies (Vo) in mediating the ferromagnetic order and spin-polarized gap states of Cu-doped ZnO nanoparticles. We demonstrate the tuning of magnetic order via post-annealing under Ar/O2. Carrier (Vo)-rich condition (Ar-treatment) is found to favor higher magnetic order of the nanoparticles with enhanced thermal stability and wide spin-polarized gap states from ultra-violet (UV) to visible energy range. Conversely, carrier (Vo)-poor condition (O2-treatment) reduces resistance to thermal fluctuations and quenched spin-polarization due to lack of carrier mediation. The proposed method is effective to tailor the magnetic order as well as the wide polarized band-gap states, of oxide opto-spintronic compounds by finding the physical equivalency between charge carriers and spin electrons.