Field-tuned crystal-field crossings provide a route to synthetic topology in localized rare-earth degrees of freedom when symmetry-resolved perturbations can independently control the crossing states. Here we show that a field-induced crossing in cubic Ce³⁺ has precisely this structure. For B∥[001], the crossing is protected by a twofold rotation, while the T_2g shears ε_xz and ε_yz break that protection and mix the two states through orthogonal pseudospin components. Together with magnetic-field detuning, these controls generate an isolated diabolical point with unit-magnitude Chern charge in a three-dimensional parameter space. Using the CeTe crystal-field scale gives an ideal single-ion crossing near 35.5 T. A calibrated point-charge calculation gives a representative projected shear coupling |α_(T_2g)|≃18.1 meV per unit tensor strain, corresponding to gaps of 0.036 and 0.072 meV for tensor shears of 0.10% and 0.20%. We identify the associated elastic and magnetic signatures, discuss the limitations of the electrostatic estimate in a hybridizing Ce compound, and determine the adiabatic and coherence requirements for cyclic geometric control. The result is a symmetry-based framework that connects high-field crystal-field reconstruction, strain response, and parameter-space topology in rare-earth systems.