You generally need a clean installation of the original GTA San Andreas to apply the mod.
While not the "Mzansi" mod specifically, subscribers to Netflix can download the official Grand Theft Auto: The Trilogy – The Definitive Edition for free on mobile devices through the Netflix app. Gta Mzansi New Horizons Definitive Edition Free
If you are looking for an official "Definitive Edition" for free: You generally need a clean installation of the