Can a specific plan be locked down?
Accepted answer
This can be achieved by 2 ways:
1. Restricting the people setting the filed against and Planned for. But this will be for all the category and Iteration setting.
2. Other way is to use the Snapshots feature in the plan that will help you take a baseline from time to time. Not just that you can compare different snapshots to know what all new is added or modified.