The magnetostructural response of a Ni-modified B2-type FeRh compound of composition, (Fe47.5Ni1.5)Rh51, is reported under the influence of simultaneous variations in temperature, applied magnetic field and hydrostatic pressure. The material undergoes a first-order magnetic transition from the antiferromagnetic state to the ferromagnetic state at a reduced temperature Tt = 144 K in the absence of applied magnetic field μ0H and applied pressure P. Applied independently, pressure and magnetic field influence Tt in opposite ways, with [dTt/dH]P=0 = −24 K/T and [dTt/dP]H=0 = 15 K/kbar, which are 3 time larger than in the parent compound FeRh. Application of Maxwell's relations to the magnetization data allows determination of the entropy change of the compound, and thus evaluates its magnetocaloric potential through the transition. Pressure application increases the magnetic entropy change (ΔSmag) but decreases the width of the magnetostructural transition, thereby decreasing the refrigeration capacity. Application of pressure also drives the phase transition to lower temperatures; it becomes sluggish and eventually is completely arrested below a critical temperature of ∼75 K. A three-dimensional (μ0H–P–T) phase diagram is constructed for the magnetic transition in the (Fe47.5Ni1.5)Rh51 system in order to evaluate the isocompositional magnetostructural response to combined application of pressure and magnetic field. Overall, these results emphasize that the magnetostructural phenomena in FeRh-based compounds is a thermally-activated process that may be tuned predictably by a variety of intrinsic (elemental substitution) and extrinsic (pressure, magnetic field, temperature) factors.