Hey Greg & Bob,
I hope you don't mind if offer some of my ideas to see if they can help. I'm thinking in terms of the books rather than the films, which may not necessarily have the same storyform. So if you are concentrating on the films, take my comments with a grain of salt!
The question of whether Frodo is a Change character really depends on exactly what his personal baggage and issues are, and the perspective those issues have given him. I skimmed the beggining of the book and it seems quite apparent that Frodo's MC throughline is about "being burdened". Even before he learns about the ring's danger, he is burdened with being the one to have to close out Bilbo's party, burdened with Bilbo's inheritance and having to divvy things up, even burdened by Bilbo's absence and the regret of not going with him. Then he becomes the ring-bearer and it's one more burden of Bilbo's that he must take on.
I think you can see Frodo's MC Concern in this quote from Fellowship of the Ring, right after Gandalf tells him his ring is the One Ring:
'...But in the meanwhile it seems that I am a danger, a danger to all that live near me. I cannot keep the Ring and stay here. I ought to leave Bag End, leave the Shire, leave everything and go away.’ He sighed.
‘I should like to save the Shire, if I could - though there have been times when I thought the inhabitants too stupid and dull for words, and have felt that an earthquake or an invasion of dragons might be good for them. But I don’t feel like that now. I feel that as long as the Shire lies behind, safe and comfortable, I shall find wandering more bearable: I shall know that somewhere there is a firm foothold, even if my feet cannot stand there again.'
So his Concern has to do with saving the Shire. And then at the very end of Return of the King, you have this:
‘But,’ said Sam, and tears started in his eyes, ‘I thought you were going to enjoy the Shire, too. for years and years, after all you have done.’
‘So I thought too, once. But I have been too deeply hurt, Sam. I tried to save the Shire, and it has been saved, but not for me. It must often be so, Sam, when things are in danger: some one has to give them up, lose them, so that others may keep them.
I would suggest that Frodo is Steadfast. His perspective is that he will never truly be able to escape his burdens, including the burden of having to save the Shire without being able to call it home again. This perspective, which has not changed but rather been cemented by his many wounds, drives him to leave Middle-Earth. (I think Judgment is still Good though -- he is happy that the Shire has been saved and happy for his friends, and doesn't regret his choices.)
But what does that mean for IC throughline, since the IC must be the Change character? I would look to Sam for that. He is all about admiring Frodo and being loyal to him. I think he starts as a Be-er but moves into a Do-er with all of his heroics, and in the end he starts a family of his own so that Frodo is not his entire world anymore. I think that is his changed perspective. He even accepts Frodo's big goodbye speech telling him he will be the Mayor and the most famous gardener in history.
Personally, I think at least for the books there is one big storyform "to rule them all", with Frodo as MC, Sam as IC, and the OS is the entire Fellowship and War of the Ring. The Frodo-Sam relationship has a lot of RS moments too, I think. Definitely there are sub-stories involved but I think that is the big overarching one.
Anyway, just my two cents focusing on the books.
P.S. While skimming I think I noticed that the First Driver is an Action -- Bilbo's unpremeditated difficulty in giving up the ring is what spurs Gandalf into thinking it really could be the One Ring, and forces him to decide to investigate that more.