49 CFR § 1111.3 - Amended and supplemental complaints.
(a) Generally. An amended or supplemental complaint may be tendered for filing by a complainant against a defendant or defendants named in the original complaint, stating a cause of action alleged to have accrued within the statutory period immediately preceding the date of such tender, in favor of complainant and against the defendant or defendants. The time limits for responding to an amended or supplemental complaint are computed pursuant to §§ 1111.5 and 1111.6, as if the amended or supplemental complaint was an original complaint.
(b) Stand-alone cost. If a complainant tenders an amended or supplemental complaint in a stand-alone cost case, the complainant shall certify that it has served on the defendant those initial discovery requests affected by the amended or supplemental complaint, if any.
(c) Simplified standards. A complaint filed under the simplified standards may be amended once before the filing of opening evidence to opt for a different rate reasonableness methodology, among Three-Benchmark, Simplified-SAC, or Full-SAC. If so amended, the procedural schedule begins again under the new methodology as set forth at §§ 1111.9 and 1111.10. However, only one mediation period per complaint shall be required.