UA Mileage upgrade on EVA Air, with status on another Star Alliance carrier
 

I apologize if this isn't the right forum, but I was thinking about using UA miles to upgrade an EVA Air flight. However, I have Star Alliance Gold status with Asiana. What I'd like to do is then subsequently apply my Asiana FF# to the flight for the base mileage and Star gold benefits. Is this possible?

Yes, the instrument used for the upgrade shouldn't affect the ffp#. I would recommend making sure you have printed BPs with the ffp you want, so that if something goes wrong you can retrocredit.