A new series of magnetoresistive oxides based on the CaCu3Mn4O12 perovskite has been investigated by x-ray absorption and neutron powder diffraction. The samples were either doped at Cu sites by Mn or by La at Ca sites. The x-ray absorption near edge spectroscopy spectra evidence the presence of two different Mn K-edges corresponding to the two notably different crystallographic environments where Mn locates. Mn3+, with localized e(g) electrons is distributed at random with Cu2+ cations at the strongly distorted A positions of the perovskite, while valence mixing Mn3+/Mn4+ occurs at the standard B site of the perovskite. The metallic behavior of the conductivity is due to the partial filling of the e(g) band of the Mn ions located at the B sublattice. The different behaviors of the two edges evidence the role of the structure on the electronic levels of the absorbing ion. Valence mixing occurs at the regular Mn(B) site of the perovskite, where no signatures of individual Mn3+ and Mn4+ edges are detected, and conversely, the energy levels of Mn ions at different crystallographic sites are decoupled.