Hi,
In EPM academy there is demo ( video) for similar requirement under Formatting -->Conditional Formatting.
This video demonstrate on how to format the columns based on selected time period. Once you do this follow below steps to just lock the cell using data validation function of Excel.
Step 1:
Step 2:
Step 3:
Result :
Using this method users can do changes only selected period and above.
Hope it helps...
regards,
Raju



