New, hybrid iron-formate perovskites have been obtained in high-pressure reactions. In addition to the pressure range, the liquid environment of the sample also regulates the course of transformations. Formate α-DmaFe2+Fe3+For6 (Dma = (CH3)2NH2+, For = HCOO-), when compressed in oil or in isopropanol at 1.40 GPa, transforms to a new phase γ, different than that obtained at low-temperature (phase β). In glycerol, phase α can be compressed to 1.40 GPa, but then it reacts to DmaFe2+For3, with all Fe(III) cations reduced, surrounded by amorphous iron formate devoid of Dma cations. Another mixed-valence framework Dma3Fe2+3Fe3+For12·CO2 can be produced from phase α incubated in methanol and ethanol at 1.15 GPa. These pressure-induced environment-sensitive modifications have been rationalized by the volume effects in transforming structures, their different chemical composition, voids, ligands, and cation oxidation states switching between Fe(II), Fe(III), their high- and low-spin states, as well as solubility, molecular size, and the chemical and physical properties of the pressure transmitting media. The topochemical redox paths controlled by pressure and the liquid environment offer new highly efficient, safe, and environment-friendly reactions leading to new advanced materials and their postsynthetic modifications.