It seems, after all we know about Chid, that he changed because his former behaviour does not fit to his momentary situation.
As Chid always tries to do the best things for himself, he now changes. There is no more need to be a Hindu ascetic, as it brings more difficulties as advantages for him at the moment.
As he seemed to have made up a religion of himself earlier and used people’s generosity for his sake, he is now in a different situation.
When he came to India, he had tried to find spiritual revelation in some way. But as his as his guru even “[stripped] him […] of his possessions including his name” (p. 27, ll. 13-15), he started living a beggar’s life – “in practice […] he found this did not work too well” (p. 27, ll.18 f.). Also in these days, he made his days easier by writing home for money if he had to and by sleeping in cheap hotels but under trees (see p. 27).
And now, as he has become ill, he is giving up and accepts that it is only the narrator who can help him. He is English after all and thus he sees that only Western standards may save his life.
He is no more able to get an advantage of his hypocrisy – it I not enough to only impress people like he could impress e.g. Inder Lal and the town’s folk, who had accepted him after he burnt his clothes and his hair.
I think Chid saw a long time ago that India was not able to give him spiritual insights. I think that was, when he told the narrator how he lives and how this came to happen. But he could keep his head above water. He did minor things that were not really conform with his “religion” that he explained people to have, because as long as he lived like that, the Indian people would accept him sooner or later, just as they did in Satipur.
That he now does not want to see or eat anything Indian might be of the feeling of strong dislike: He reached none of the targets he wanted to reach in India. His returning illness was now the straw that broke the camel’s back: He is no longer willing to play the role that he made up for himself to survive because he realized that in it, it is no longer possible to survive.
Returning to the narrators and Inder Lals home he finally admits that he is a Western man and has to live in those standards. He can not change himself. And, summing all the theses up that I wrote into my text, he does not change at all, because even at the time he had been an ascetic, he had not been entirely different from what he is now: The only difference now is that he allows his “Western behaviour” to be visible on the surface. He plunked his role and is therefore braking every up every connection from his life to his role, beginning by no more eating Indian food and stopping at becoming silent (again?).
Leaving this senseless stuff uncommented proves the non-reading of certain persons… 
