19 CFR § 144.1 - Merchandise eligible for warehousing.
(a) Types of merchandise. Any merchandise subject to duty may be entered for warehousing except for perishable merchandise and explosive substances (other than firecrackers). Dangerous and highly flammable merchandise, though not classified as explosive, shall not be entered for warehouse without the written consent of the insurance company insuring the warehouse in which the merchandise is to be stored.
(c) Merchandise previously entered. If merchandise has been entered under other than a warehouse entry and has remained in continuous Customs custody, a warehouse entry may be substituted for the previous entry. If estimated duties were deposited with the superseded previous entry, that entry shall be liquidated for refund of the estimated duties without awaiting liquidation of the warehouse entry. All copies of the warehouse entry shall bear the following notation: This entry is in substitution of ____________; entry No. ______, dated ____________.