. . "rus brandy or alcohol, but without any other addition or abstraction except as may occur in cellar treatment: Provided, That a domestic product may be ameliorated or sweetened in accordance with the provisions of 26 U.S.C. 5384 and any product other than domestic may be ameliorated before, during, or after fermentation by adding, separately or in combination, dry sugar, or such an amount of sugar" . .