Under what circumstances can a unilateral modification be used?

A unilateral modification can be employed primarily for issuing change orders and making administrative changes. This type of modification allows one party, typically the government or contracting officer, to make changes to the contract without needing the other party's consent. Change orders often occur when work needs to be adjusted due to unforeseen circumstances, or when there are minor changes in the specifications that do not affect the overall scope or contract price significantly. Administrative changes might include corrections to typographical errors or updates to contact information.

In contrast, adding new line items, negotiating cost reductions, or extending contract duration typically requires mutual agreement between both parties. These actions involve changes to the fundamental terms or scope of the contract, which cannot be executed unilaterally without the consent of the contractor. Therefore, the correct answer reflects the specific scenarios where unilateral modifications apply, emphasizing procedural efficiency and the ability to manage minor adjustments without lengthy negotiation processes.