Sure, Pegasus has this option.
Select the identity you created for your Yahoo account.
Go to your internet settings for this identity.
Select the POP3 and/or SMTP Tab.
Double-Click on the server, the config dialog will appear.
Here you can change the port number, in the second tab ("security") you can enable SSL. (Note: Pegasus changes the ports automaticly, if you use SSL)
Hope this will help you.
kind regards