Below is a post I saw on the CCNA Prep Center discussion forums....
Hi. The router simulation assessment items are very "high fidelity" representations of the work environment present for the tasks assigned in the certification exam. That is, for the requirements of the test item, the router IOS should offer every command and support every procedure that is reasonably required to accomplish the task. So in answer to your question, the "no" form of a configuration command is supported as a way of undoing a configuration.
As to saving your configuration before leaving a test item, it is not necessary to save a configuration before moving to the next test item. If it were, we'd be certain to reinforce that fact in the test item directions, simulation software, and sample items. We don't want you to waste your hard earned points!
Regards,
Martin
I like the way he put it "We don't want you to waste your hard earned points!".... Thanks!
2lbs.