Some people suggest that you export the Yahoo Address Book as LDIF format, but the thing with this is that you lose all your contacts’ home email addresses.
To keep all your work and home email addresses, you can use the script I wrote: https://www.spudart.org/php/yahooaddressbook2vcard
It will convert over the following fields from Yahoo into Mac OS X Address Book:
–Alternate Email 1
–Alternate Email 2