How to prohibit to make changes of planned data

Hi, folk!

I've faced with the following issue. After complete monthly planning process I have to prohibit to make any changes for all users for current month and year. But at the same time I have to left permission to make any changes for 2-3 users with role Financial Director.

Please give me advice, how to implement mentioned functionality?

Of course, I can revoke permission to start corresponded planning folders, but... To start planning process for the next month I have to grant mentioned permissions.