I honestly wouldn't be too bothered if they replaced the Holm version of Bilbo finding the ring with the one they made with Freeman for the Hobbit. Partially because, if they want to go for relatively seemless continuity between the two series (which it seems like they definitely do) it would make sense to insert The Hobbit version into Fellowship.
But mostly because, unlike the whole Return of the Jedi Haden Christensen fiasco, Holm is present in a large chunk of the movie after that scene. Replacing him in one five-second scene wouldn't exactly be robbing him of a ton of his screen time. Plus, he's be playing old Bilbo again in The Hobbit anyway.
Then again if they choose to keep the original scene and simply make him look a bit younger digitally or just not touch it up at all, I'd be fine with that too. But I think they'd be justified in replacing the original scene (but keeping it on the disc, of course

)