We demonstrate a novel wide-frequency tuning mechanism for superconducting microwave cavities designed for dark matter searches. Using a Nb${}_3$Sn-coated cigar-shaped cavity operating at approximately 9,GHz, we achieve continuous frequency tuning exceeding 1,GHz by mechanically separating the two cavity halves: a “tuning-by-opening” technique. Finite-element method simulations predict that radiative losses do not degrade the quality factor even for large openings, as a closed cavity with an intrinsic quality factor of ${10}^7$ maintains this value for apertures up to 9,mm, corresponding to a tuning range from 9.0 to 7.5,GHz. Experimental validation using both copper ring spacers and a continuous sliding mechanism confirms $Q_0$ values exceeding the dark matter quality factor across the entire explored frequency range, despite mechanical imperfections and film non-uniformities. This tuning approach avoids inserting elements into the resonant volume, making it particularly suitable for high-Q superconducting cavities in axion haloscope experiments and readily applicable to REBCO-based implementations capable of operating in multi-tesla magnetic fields.