You load Actual data to the Actual category that will be locked by work status after loading.
Then you copy from Actual category to FC category the required months.
For FC category you also lock Actual moths with work status. In addition to work status lock (will reject any attempts to write data) it's better to prevent data entry on the template level.
I prefer to use Excel Data validation using formula: to compare the column number with the PLANMONTH property of FCx category (can explain details)
Vadim