As of Control 04.60.1205.xxxx, you can configure Control to lock the general ledger to prevent changes in prior time periods.
These setting are located in the Close Out Options screen, in Accounting Setup.
You have the option of locking the ledger for before:
If necessary, this lock can be temporarily disabled by click the button the says “Allow prior period GL changes on my session until I log off”. When clicked, the lock will be disabled for only this user and will be re-enabled when the user logs off. The lock can be re-enabled for clicking the button again at any time.
The following restrictions are put in place when the lock is enabled: