What is the primary use of unilateral modifications in federal contracting?

The primary use of unilateral modifications in federal contracting is to issue change orders, which is why this answer is the most applicable. Unilateral modifications allow the government to make changes to the contract without the contractor's agreement, particularly for actions that need to be taken promptly or are within the scope of the contract as defined by certain clauses.

In the context of federal contracts, unilateral modifications can include administrative changes, changes to the delivery schedule, and changes in the quantities of supplies or services, which constitute typical change orders. They serve the government’s need to enforce its rights under the contract terms efficiently without needing to negotiate with the contractor every time a minor change is necessary.

The other options relate to various actions that can be taken in federal contracting, but they do not capture the primary function of unilateral modifications. For example, while termination notices are important, they are typically a separate action based on a non-compliance or need to end the contract rather than a modification. Similarly, changes authorized by clauses other than a changes clause typically involve bilateral modifications, where both parties must agree. Thus, option C succinctly identifies the main purpose of unilateral modifications in this context.