Tunable valley polarization and spin splitting in altermagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi mathvariant="normal">F</mml:mi> <mml:msub> <mml:mi mathvariant="normal">e</mml:mi> <mml:mn>2</mml:mn> </mml:m

The altermagnetic state combines broken time-reversal symmetry with compensated magnetic order to generate spin-split bands at zero net magnetization and offering promising spintronic functionalities. In this work, we use first-principles calculations to demonstrate deterministic control of valley and spin states in two-dimensional altermagnetic $\mathrm{F}{\mathrm{e}}_{2}\mathrm{Mo}{\mathrm{S}}_{2}{X}_{2}$ ($X=\mathrm{S}$, Se, Te). Monolayer $\mathrm{F}{\mathrm{e}}_{2}\mathrm{Mo}{\mathrm{S}}_{2}\mathrm{S}{\mathrm{e}}_{2}$ exhibits giant strain tunable valley polarization (58 meV at 4% tensile), while $\mathrm{A}{\mathrm{A}}^{1}\ensuremath{-}\mathrm{stacked}$ bilayer $\mathrm{F}{\mathrm{e}}_{2}\mathrm{Mo}{\mathrm{S}}_{2}\mathrm{S}{\mathrm{e}}_{2}$ show electrically programmable spin splitting (105 meV and 133 meV in X/Y valleys at ${E}_{z}=0.1\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\AA{}$). Spin-flip switching, enabled by magnetic moment reversal and detected via magneto-optical Kerr contrast, emerges as a distinct phenomenon in bilayer $\mathrm{F}{\mathrm{e}}_{2}\mathrm{Mo}{\mathrm{S}}_{2}\mathrm{S}{\mathrm{e}}_{2}$. These findings establish two-dimensional altermagnetic $\mathrm{F}{\mathrm{e}}_{2}\mathrm{Mo}{\mathrm{S}}_{2}{X}_{2}$ ($X=\mathrm{S}$, Se, Te) as a platform for valleytronics, with design principles applicable to ultra-low-power spintronic devices.