27 C.F.R. § 19.391 – Mixing denatured spirits.

(a) Spirits of the same formula. If a proprietor has two or more different batches of denatured spirits produced under the same formula, the proprietor may mix them on bonded premises.
(b) Spirits of different formulas. A proprietor may mix denatured spirits produced under different formulas on bonded premises for immediate redistillation at the same plant or at another plant subject to the provisions of §§ 19.314, 19.315, and 19.316.
(26 U.S.C. 5241, 5242)