Arranging the stacking orders of $A$-type antiferromagnetic ($A$-AFM) bilayers offers a practical pathway to realizing two-dimensional altermagnets. Previous proposals, however, rely on stringent symmetry constraints, including layer groups and stacking registries. In this work, we demonstrate that circularly polarized light (CPL) irradiation breaks time-reversal symmetry, enabling altermagnetism possessing collinear magnetic moments without these restrictions. Our comprehensive symmetry analysis reveals that inversion-symmetric $A$-AFM bilayer building blocks can host altermagnetism that is robust against stacking slides and variations in illumination direction, with rich and continuously tunable symmetry representations. Using bilayer ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ as a case study, we show that out-of-plane CPL stabilizes distinct $f$-wave or $p$-wave altermagnetic states in forward stacking, while reverse stacking manifests an even-odd parity conversion of altermagnetism based upon specific sliding configurations. These revealments broaden the scope of altermagnet design in inversion-symmetric $A$-AFM bilayers and establish CPL as a versatile control knob for engineering altermagnetic symmetries.

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• Magnetism
• Photoinduced effect
• van der Waals systems
• Spin
• Bloch-Floquet theorem