The impact of the changes is to shift the focus away from the Matthean temple imagery and more directly to the Savior. In the New World context this is entirely appropriate as the people appear to have had greater access to the temple than in the Old World. What they have in the New World case, is the Messiah standing before them. Of course the risen Savior is the person to whom the sacredness of the temple looks, and it is quite appropriate to use his presence to focus their understanding.
The way in which the changes are made also confirm that the alterations are made against the KJV English text. In particular, there is a rather artful blending of insertions, deletions, and retentions in verse 24 to retain as much as possible of the KJV verse structure while still making desired changes.