Hi

Try using Data/Text to columns.
Select the column and click on Data / Text to columns. On the first two
dialog boxes, click next. On the third dialog option box, in the top right
corner, tell Excel that the column is a date and the format of that date.
Job done! Make sure you take a copy before you start.

Hope this helps.
Andy.

I don't know how you download your data, but you may want to try this:

Save the download into a plain old text file (*.txt).

Then when you open that text file in excel, you'll be prompted to describe each
field.  You'll be able to choose Text for that field with the expiration date.
So excel won't change it to a date.