Spin-orbit torque efficiency is conventionally fixed by bulk materials. $D$-wave altermagnets introduce an additional nonrelativistic spin-charge conversion channel beyond the inverse spin-Hall effect. Using prototypical candidate ${\mathrm{RuO}}_2$ as an example, we show that the adjacent ferromagnet alone can dictate both the magnitude and sign of spin-charge conversion. Spin-pumping measurements on ${\mathrm{RuO}}_2/{\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG) and ${\mathrm{RuO}}_2/{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ (Py) bilayers yield opposite effective spin-Hall angles that persist across crystalline and polycrystalline ${\mathrm{RuO}}_2$. Inserting an ultrathin Au spacer at the ${\mathrm{RuO}}_2/\mathrm{YIG}$ interface reverses the signal, evidencing a dominant interfacial inverse Rashba-Edelstein effect, whereas ${\mathrm{RuO}}_2/\mathrm{Py}$ is governed by the bulk inverse spin-Hall effect. First-principles calculations trace this dichotomy to interface-selective band hybridization: Rashba surface states survive at the insulating YIG contact yet are quenched by metallic Py. Our findings establish ferromagnetic interfacing as a deterministic knob for tailoring spin-charge conversion in altermagnetic oxides, paving the way to field-free, low-dissipation spintronic memory devices.

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• Spin current
• Spintronics
• Altermagnets
• Magnetic multilayers
• Ferromagnetic resonance
• First-principles calculations