You need to use Directory Export and Import, with a little manipulation of the data between. Excel is good for the data manipulation, as the Export and Import use CSV files. You'll need to be careful, because your new data will include a comma, which is the field separator in a CSV file (Excel should cope, though, it will create the fields with commas in them with double quotes around the field, and Import understands this).
If you're unfamiliar with Directory Export and Import, you need to be careful - you can really screw your directory up big time if you get it wrong. See
for a good overview of the process, it also include links to other relevant articles. Have a few test runs on a testbed server first so that you're confident it will work in production when you do it there.
You can Export a container without having an existing header file, you then get a bunch of default columns. You can remove columns you're not changing, but leave the first column, the Display Name column, and the Directory Name column. In an unused column put a formula something like this: =RIGHT(B2,LEN(B1)-FIND(" ",B2))&", "&LEFT(B2,FIND(" ",B2)-1) This assumes your display name is in column B, if not change the references accordingly. It doesn't start on Row 1 because that's your header row. Drag the formula down and you should change all your Display Names round.
However this means you now have two Display name columns, the old and the new. You can't import like this, and you can't remove the old because the new depends upon it. You can either ‘Copy’ and then ‘Paste Special, Values’ the new column to fix it to text (instead of a formula), or you can Save As a CSV, then close and open the file. Either will remove the formula from the new display name column, you can then remove the old Display Name column.
When doing this sort of Import I like to use a Mode column (always the second column of an Import if it is used). You want Modify for every line other than the header row for the Mode column.
