Changing the range for averages with out changing the formula.

Hi

I would like to create a column to list cells that would be excluded from an
average. I don't want to change the formula because I want to lock those
cells. Is this possible? The main reason I want to lock the formula is
because I want it to be clear if any values are excluded.

Example of what I have:

Columns A Text descriptors
Columns E:Z numbers to be averaged (sourced from several other sheets,
includes many blank cells, locked)
Column AA: =Avg(A:Z) (locked)
Column AB: =Stdev(A:Z) (locked)
Column AC: =AB/AA (locked)
Possible Column AD: cells that should be excluded from the average, not
locked. For example AD3: =B3 or be blank.

How could I rewrite AA and AB to take into account AD and not include those
values.

Other should have some freedom to remove outlying points based on the
standard deviation and COV but I want it to be very clear what points they
excluded and easy for others to play around with excluding different values
or no values.