/**
     * Converts existing Attribute to different type
     *
     * @param  Mage_Catalog_Model_Entity_Attribute $attribute     Attribute
     * @param  string                              $backendType   New Backend Type
     * @param  string                              $frontendInput New Frontend Input
     * @return void
     */
    protected function _convertBackendType($attribute, $backendType, $frontendInput)
    {
        $_dbConnection = Mage::getSingleton('core/resource')->getConnection('core_write');
        $newFrontendInput = $this->_getFrontendForBackend($backendType, $frontendInput);
        if ($newFrontendInput) {
            $frontendInput = $newFrontendInput;
        }
        // Actual Conversion of Attribute
        $sql = <<<EOS
UPDATE
    eav_attribute
SET
    backend_type = ?,
    frontend_input = ?
WHERE
    attribute_id = ?;
EOS;
        try {
            $_dbConnection->query($sql, [$backendType, $frontendInput, $attribute->getId()]);
            // Migrate existing Data
            if (!in_array($frontendInput, ['select', 'multiselect'])) {
                $this->_migrateData($attribute, $backendType);
            } else {
                $this->_migrateSelect($attribute, $backendType, $frontendInput);
            }
        } catch (Exception $e) {
            $this->_getHelper()->log(sprintf('Exception occured while converting Backend Type'), $e);
        }
    }