How do I change a 3D box collider during an animation?

I don't know any good ways of changing the box collider for my character during its jump animation and after doing some research, I decided to use the Animation Window. It took forever to even access the animation from the drop down because it was Read Only.

But now that I've gotten to it and figured out how to add the box collider size and center as a property to edit during the animation, it won't work. I want to edit the collider through the values in the Animation Window by also looking at the animation in the Scene view, but every time I press play in the Animation Window, I get a ton of errors saying "NullReferenceException: The Playable Output is null." I feel like wanting to change the collider size during an animation shouldn't be too hard because it doesn't sound that hard. But just getting to this point has been nothing short of ridiculous, and I'd be lying if I said I wasn't getting frustrated.

I can't find a single resource online showing how to edit a 3D box collider to change in size during an animation.
Can anyone help!