Chapter 10 is a more complex chapter than it seems to be and it can be argued that the chapter indicates no change in Frederic Henry's views at all. What do we know and what does Chapter 10 show?
We know that Henry, an American, voluntarily enlisted in the Italian war and that he may have liked to enlist in the British army, though this point is vague and only painted as a shadow of a hint when in Chapter 5 he talks with the head nurse (when looking for Catherine) about his place in the war. Henry tells her his stated reason for joining the war with the Italian army: "I was in Italy, and I spoke Italian."
... "there's a war on, you know."
I said I knew.
"You're an American in the Italian army? ... How did you happen to do that? Why didn't you join up with us?"
"I don't know," I said. "Could I join now?"
"I'm afraid not now. ... Why did you join up with the Italians?"
"I was in Italy," I said, "and I spoke Italian." (Chapter 5)
Whether he had a deeper reason than proximity and language skill for joining the war, we don't at this point know. We do know that as time passes and his penetration in the war becomes more significant--like seeing the platoon of Italian soldiers pass him with the "stragglers" who couldn't keep pace coming behind and the soldier with the lost truss and the ruptured hernia who already had been denied medical treatment on the presumption that he had lost his truss intentionally coming up, limping, even further in the rear--his expressed opinion of the war he has voluntarily joined is that it is "Rotten."
"How do you like this g--d--m war?" [he said].
"Rotten," [I said]. (Chapter 7)
Assuming that Henry joined for some deeper reason than those stated above, it can be argued that his views on the war have changed by Chapter 7, though there is no indication in the text that his views are any different in Chapter 10 than they are in Chapter 7. While Henry denies heroism in Chapter 10 when Rinaldi enthusiastically, yet in his typically teasing way, informs Henry about his sponsorship for an Italian medal of honor, the "medaglia d'argento," he doesn't say or do anything that indicates his views toward the war. The only indications this conversational exchange provides us is insight into Henry's characteristic humility and stoical detachment.
When Catherine is brought into the conversation, Rinaldi is sincerely, though typically jauntily, speaking about her and Henry, though he perhaps goes too far by saying that British goddesses are no good for anything to a man except to be worshipped, implying that British women are of no sexual value to a man and that she is cold and distant like a marble goddess. This seems to annoy Henry (although being told he is "purer and sweeter" may have already annoyed him by casting dispersions on his manhood) since Henry is pleased the see that the word "stupid" wounds Rinaldi's feelings. He thus repeats it until Rinaldi lashes back at which point Henry recants and says, in his typically detached manner, "Don't get angry." Since Henry never had the same response to the talk about women that went on between Rinaldi and the other officers and since it is in Chapter 7 that Henry expresses his first sincere emotional reaction toward Catherine, it can be argued that this conversation between him and Rinaldi does not indicate a change in his views about women as that change began much earlier:
I had treated seeing Catherine very lightly, ... but when I could not see her there I was feeling lonely and hollow. (Ch. 7)
Similarly, in Chapter 2, when the first young priest is introduced, Henry never entered into the teasing the priest was subjected to by the other officers. Instead, he smiled at the priest, accepted his conversation and was respectful toward him. If at this point Henry's attitude toward priests can be equated with his attitude toward the Church, then it can be argued that there is no change in his views indicated in Chapter 10 based on "I like him" because this is exactly the sentiment he expresses about the first young priest from Abruzzi--whose family Henry wanted to visit while on leave, though he was psychologically unable to actually act to get himself there--when he speaks about him in Chapters 2 and 3.
I smiled at the priest and he smiled back ... we were still friends .... (Chapter 2 and 3)
But if you must analyze Chapter 10 as being a turning point in Henry's views, you might say that being injured in the midst of dead or dying comrades has moved him toward feeling absurdity in the war; has confirmed his growing view of the value of a woman's devoted love; and has confirmed his positive feelings toward his priest acquaintances and toward the Church represented.
As Frederic has this conversation with Rinaldi, he is in hospital, having been wounded. What is so interesting about this conversation however is the way in which Frederic now shows no interest whatsoever in gaining a medal or recognition for being wounded in war. Note how Rinaldi tries to tell him that he will be given a medal for being wounded, and tries to ask him if he did anything heroic in the way he was wounded. Frederic's rather deadpan response indicates his lack of interest in receiving any military recognition whatsoever:
"Did you do any heroic act?"
"No... I was blown up while we were eating cheese."
His complete disinterest in receiving any medals shows his change of heart towards war, and this is also matched by his change of attitude towards religion, which is indicated when he acknowledges that he likes the priest, and also the way in which he begins to take the idea of a loving relationship with a woman more seriously. What seems to cause the two characters to argue is when Rinaldi begins to tease Frederic about his relationship with Catherine. Frederic possibly feels that there is something different about what he has with Catherine compared to Rinaldi and his endless exploits, indicating that he is beginning to contemplate a serious, committed relationship, and feels that there is more to love than just meaningless visits to the brothel. Chapter 10 therefore is quite a key section of the novel in terms of the differences in the central character that it suggests, and how he is changing.