In this paper we study the post‐synthetic modification (PSM) reaction on solid spin crossover (SCO) [Fe(NH 2 trz) 3 ]X 2 (X = NO 3 , OTs, Cl, SO 4 , BF 4 ) complexes with different substrates. The wide access to a diversity of functionalized complexes with imine, amide and carbamide groups from the same amino parent compound demonstrates the synthetic approach value of this method. The as‐obtained post‐synthetic complexes were studied by IR, solid NMR, elemental analyses and powder X‐ray diffraction, and compared to the corresponding compounds obtained by direct synthesis (DS) routes. Moreover, after digestion of the complexes obtained by PSM reactions, the free ligands were characterized by NMR in solution, which allowed us to indirectly confirm the formation of complexes we wished to synthesize. The study reveals in numerous cases that a complete post synthetic modification is possible despite the structural cohesion that is established between the 1D coordination chains within these materials. Spin crossover properties of some complexes obtained by both methods are also reported and compared.