Classes/Console/Core/Booting/Scripts.php
public static function overrideImplementation($originalClassName, $overrideClassName)
    {
        self::registerImplementation($originalClassName, $overrideClassName);
        $GLOBALS['TYPO3_CONF_VARS']['SYS']['Objects'][$originalClassName]['className'] = $overrideClassName;
        class_alias($overrideClassName, $originalClassName);
    }
public static function overrideImplementation($originalClassName, $overrideClassName)
    {
        self::registerImplementation($originalClassName, $overrideClassName);
        $GLOBALS['TYPO3_CONF_VARS']['SYS']['Objects'][$originalClassName]['className'] = $overrideClassName;
        class_alias($overrideClassName, $originalClassName);
    }
Tell Extbase, TYPO3 and PHP that we have another implementation

@param string $originalClassName
@param string $overrideClassName