Framework modification by doping of Fe3+ ions in C12A7 has been recently considered for tailoring its thermal, electronic, and optical properties. Here, we use density functional theory calculations to predict the thermodynamical stability and electronic structures of a single Fe atom encapsulated and substituted by both stoichiometric and electride forms of C12A7. In both forms, exoergic encapsulation is observed, and the resultant complexes exhibit magnetic behavior inferring that they are promising magnetic material candidates for spintronic devices. While the electride form of C12A7 transfers 0.86e to Fe, only a small amount of charge (0.14e) is transferred from Fe to the cages in the stoichiometric form. Substitution of Fe for Al in both forms of C12A7 is endoergic, and the electride form is more favorable by 1.60 eV than the stoichiometric form. Both encapsulation and substitution introduce Fe sub-bands between the top of the valence band and the Fermi energy level, featuring them as promising materials in catalysis, optics, and electronics.