I don't think he would've even had to have changed his face. The Founder is infamously reclusive. So much so, that he doesn't even attend his business meetings. Leading up to Orion's surprise meeting with him at the party, it's implied that it had been at least a few years since any of his business partners had seen him and that his public persona is even more reclusive, so Orion may be the only character in the game so far to have seen The Founder's face. If other characters know him under some other personas, they wouldn't even know with so few people having seen him since starting Eternum. I don't personally think The Founder is Nancy's ex, but if he was there would be no way to know at this point in the game. I think The Founder will end up revealing some personal connection to Orion. I don't know what it's going to be, and I think that once the revelation comes there'll be a 50% chance it's a lie to manipulate Orion, but that kind of play is pretty on brand for the kind of megalomaniacal antagonists that The Founder seems to be