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The point of view of a story is the point from which the reader experiences the story. What you do with point of view should be based on what the reader will want to experience at any given point in the story. 

I often see writers decide on a point of view long before they have figured out what the object in view is, and where the reader will need to stand in order to experience the object in view as they wish to. This is to be a slave to convention when you should be a slave to the reader. 

Will a change of point of view late in the novel, or at any point in the novel, seem jarring to the reader? No, what will see jarring to the reader is not being able to see the things they want to see, to experience the things they want to experience. 

If the reader has to climb a tree to see the parade pass buy, by all means have them climb a tree so they can see the parade pass by. But if the reader wants to see a lovers' kiss, for God's sake get them out of the tree first so they can see properly. 

By the same token, though, what is your desire to keep the POV with the first protagonist based on? Is that going to be the single POV that will provide the reader with the best vantage point for all that they want to see for such a long stretch of the novel? If it is, that's fine. And if the switch to the second POV is, equally, putting them where they need to be to see the rest of the action, that's fine too. 

But if you are keeping the reader from the place they want to be to see the parade in the first half or switching them to a place they don't want to be to see the lover's kiss in the second half, they are not going to be happy with you.