Honestly, I would just prefer to shoot the whole film with the same camera and aspect ratio as I like consistency. I's probably wouldn't have much of a problem with it if it was one of the spinoff films, but this a main episode. It should be more consistent with the original visual style.

BUT, if they have to do it. It should just be one long continuous sequence that changes at a climactic or emotional point. I like how Catching Fire did it (seen here), with having the aspect ratio change make sense somewhat logically in terms of the plot. Also, the shot is dark enough and the bars change slowly enough for it not to be painfully jarring. In the IMAX theatre, it was a true WOW moment. Plus it continued that way for 50 full minutes till the whole arena sequence was complete and they even had the character pass out, between the aspect ratio change back to 2:35:1.