Conditional Format To Lock Cell

Hi,

I run some forecasting sheets for my work using excel, and have come
across a problem.

Basically there are multiple columns with each customer, and multiple
rows with week 1 to week 52. The people in charge of forecasting must
finalise their predictions 5 weeks in advance. I have written a
conditional formula that makes the cell grey if that cells date is
less than 5 weeks away. However I would really prefer to have this
cell locked, and passworded.

Is there any way of doing this?

Additional information:

The first cell this applies to is T11. (down to T62) Then rows Z, AF,
AL etc all way until ED.

Thanks in advance,

James