I think as long as it's clear to the reader that the change of pronoun is for a reason and not an error on the part of the writer, I think that's definitely within bounds. Consistancy being the key. As long as Nepetu is "he" in every reference up to that point and then "it" in every reference thereafter, I'd say you're safe. Does that make sense?

If you're doing this for the reason I'm guessing, I think it will be a powerful statement. And will tie in perfectly with a similar choice I made in "The Cat".