What action is prohibited by the 3rd General Order?

The third General Order specifically states that a sentry is to "report all violations of orders I am instructed to enforce." This establishes the importance of adhering to the assigned responsibilities without unauthorized alterations to one's duties, such as changing a post location. Therefore, the action of changing the post location without permission is prohibited because it undermines the chain of command and can lead to security breaches or other operational issues.

The other options pertain to different aspects of a sentry's duties, each of which addresses specific responsibilities that are equally important. However, they do not directly reflect the prohibition outlined in the third General Order regarding unauthorized changes to post duties. Therefore, the focus on maintaining the integrity of one's assigned position without deviation is the essence of the prohibition associated with the third General Order.