You can get that specific count for your manager one of two ways. Safely:

SELECT COUNT(*)

FROM MyTable

WHERE MyColumn = 'OldValue'

Or not so safe:

BEGIN TRAN

UPDATE MyTable

SET MyColumn = 'NewValue'

WHERE MyColumn = 'OldValue'

ROLLBACK TRAN

The first query will return the count. The second query will return the number of rows affected, but it won't do anything. However, you are mucking with the data, just rolling it back, so you will put a load on the system. It's not as safe.