There is no setting yet to disable the function to change the acceptance status by chairs and track chairs. Up to now, we haven’t heard about such problems in practice.
But if you are concerned, you can use an alternative solution. Please go to:
Overview => Settings => Manage Acceptance Status
… and edit each available status affected. For each status click on "Edit". On the page that opens, scroll down to the option "Assignment Rights" and uncheck the box "Chairs / track chairs can assign this status to contributions" (see image).
Please don’t forget to test your settings.