Fixed height of rectangle in box select mode possible?

I’m implementing a custom range select event where I don’t need the range or points of the y-axis. It should act like the default zoom mode with Layout.yaxis.fixedrange = true.
Is it possible to fix the rectangle which is drawn when selecting an area on the plot in box select mode to a specified axis?

Not via the API at the moment unfortunately.

You can try forking the repo and tweaking this parameter.