An agency may amend a solicitation after the deadline for receiving offers, so long as the amendment is not “so substantial as to exceed what prospective offerors reasonably could have anticipated” in submitting offers under the original solicitation.
This rule, which is codified at FAR 15.206(e), was at issue in a recent GAO bid protest decision, in which the GAO held that the amendment merely clarified the original solicitation and thus did not require cancellation.