For future use, I find it helpful to modify the subject line in e-mail that I receive in MS Outlook. Although the subject line is grey, it is not "grayed out". The subject line is editable.
Simply open the received e-mail, place the cursor in the subject line, and make any needed changes. Click on the Save icon or on File/Save and you are done. This method probably works in all versions of Outlook and may work in Outlook Express
Although I am sure I am not the first person to discover this, I did discover this "feature" on my own.