Thanks for the responses. I was able to call and get the AS EUG-PDX-LAX routing I wanted. The original AA nonstop EUG-LAX was ridiculously high (hence why I paid for F to begin with), so even with the change fee, it ended up being $12 cheaper.

Now, I also called again to get the PNR for my AS half of the ticket (how annoying, that's information that's easily available on UA and AS websites, but I digress). Do you think if I put my AF mileage number in there, the miles will eventually credit to AA and not AF?