The sustainment of field-reversed configurations through controlled magnetic merging is investigated using three-dimensional Hall magnetohydrodynamic simulations. Motivated by experimental demonstrations of tilt-stable field-reversed configuration (FRC) formation via counter-helicity merging, this study explores the impact of intermittent injection of spheromak and FRC-type plasmas into a pre-formed FRC core. Two merging strategies are considered: (i) the injection of compact spheromaks and (ii) the merging of externally generated FRCs. The results indicate that spheromak-FRC merging produces localized reconnection and strong bi-directional toroidal shear flows, which effectively suppress the n = 1 tilt mode and generate significant ion heating. In contrast, FRC–FRC merging yields weaker reconnection-driven flows and reduced thermalization, resulting in lower ion temperature increments and incomplete suppression of global MHD instabilities. A parametric study of the injection (compression) speed reveals a trade-off between energy deposition and stability, with optimal performance observed at intermediate velocities.