In most cases, no. But there are some instances when the system might allow additional entries for a specific field. And if you're wondering whether you can add your own fields for a contact entry, check this out.

If you use the Clean up Duplicates function, the tool will show you any contacts for whom you list multiple entries for a specific field. You can keep all these entries if you want!

You can also view and edit these additional fields at http://address.yahoo.com—just click Edit to edit or remove them. Currently, you can’t view or edit these additional fields in Contacts in the new Yahoo! Mail.