Per the Wikipost at the top of the page: You could try changing your FFN by:
Calling
DMing [MENTION=450792]AmericanAir[/MENTION] on Twitter (see
https://www.flyertalk.com/forum/amer...aster-thd.html)
Try using the Finnair website
Having the FFN changed at the airport
You are supposed to get the benefits of the airline you are crediting to, so no courtesy upgrades- you can’t have your dessert and eat it too.