Modifying every item in a column

YOu can probably do this easiest with a macro someone could provide. A more manual approach would be as follows if you wanted to add an "A" in front of everything in column A.
="a"&A1
copy this down as far as you need.
You could now copy and paste special value your new column and delete A if you like.

Good Luck

If you wanted to do it via VBA then;

Sub Add_A()
Dim DataRg As Range
Dim data As Range

Set DataRg = Range("A:A").SpecialCells(xlCellTypeConstants, 23)

For Each data In DataRg
If data <> "" Then
data = "A" & data
End If
Next
End Sub