Hi Uruj,
I have 1 idea as below.
If you want to disable timesheet adjustment, you will need to make "Time Reporting Periods" of desired timesheet Close.
The time periods are a global level.
So, after you closed some time periods, all users will not update timesheets of that periods.
If you need to adjust the timesheet which time period is closed, you will need to re-open time periods, and adjust timesheet and then close it again.
Regards,
Shoichi