If you are a Test manager and want to prevent manual testers from changing the Test Plan, you can set up permissions in TFS to do this.
1. Right mouse click on your Team Project > Team Project Settings > Areas and Iterations
2. Select Area and click on Security button on the bottom
3. Select Testers group and Deny “Manage Test Plan” permissions
4. So now manual testers will not be allowed to create, edit or delete a test plan in Microsoft Test Manager. If a manual tester tries to create/edit/delete a test plan, they will receive the following message that prevents them from doing so.