27 CFR §25.94

1. (a)Requirement. When the penal sum of the brewer's bond (calculated as provided in § 25.93) in effect is not sufficient, the principal may prepay the tax on beer as provided in subpart K of this part, or give a strengthening bond in sufficient penal sum if the surety is the same as on the bond in effect. If the surety is not the same, a new bond covering the entire liability is required.
2. (b)Restrictions. A strengthening bond may not in any way release a former bond or limit a bond to less than the full penal sum.
3. (c)Date of execution. Strengthening bonds will show the current date of execution and their effective date.