In another column, in the first cell type this:
="manco_"&A1
Replace A1 with whatever the cell is that has your information to be modified. After you see that this is providing you the right information, fill this data down to all of the other cells below it. Now, copy that whole column, and go to the column that has your original information and do a Paste Special and select Values. Now go back to the column that you had previously entered the formula in and delete it, since it will now say manco_manco_1234-10.
TD