Help desperately required.

I have a spreadsheet that takes a collection of user inputs to generate a
value that managers in my org will use as a guide to providing promotional
increases to employees. However, managers have the flexibility to choose a
different value if they want and so directly below the calculated cell value
is a free cell that managers can make their actul recommendation in.

Only trouble is.....this free cell is linked to some of the original
variable inputs that created the original input and so, depending on what
value the managers choose to enter, the original recommendation can change
and I don't want that.

So, problem of the day is as follows:- is there any way in excel to freeze a
cell value once it has been calculated for the first time so that any further
changes to input variables will not change the answer?

Many thanks