Actually, I don’t think you can kill it that easily, but it may become so ungainly that you’ll decide to take it out anyway! I realized after posting that I probably suggested doing pretty much what you were thinking, so we may both be wrong … (I’ve gotten used to it.)
Another approach would be to cut it back to one of the more vertical laterals low down on the tree, and then train that lateral to become a new central leader by pulling it up by binding it to the tree trunk. That might work pretty well.
But that wasn’t your original question as to when to graft. I always wait until the leaves on the tree are “the size of a squirrels ears”. The point is that you want to catch the tree in a good flush of growth, with lots of sap flowing, early in the season in this case. Think seventh graders.
I hope you have a ton of fun- and even if it fails completely you’ll only be the wiser for trying.
Good luck,
M