OK. I had never seen this technique before, but it makes sense in this application!
The fusible is usually not removable. If you are machine quilting, it will be no problem to machine quilt through it. If you are hand quilting, you might want to find a way to avoid the fusible. If you do have to hand quilt through it, it is going to be more difficult than normal and you might have to quilt one stitch at a time (or stab stitch just in one direction at a time!). It's not impossible to do; just a little harder.
You could try removing the fusible by warming it and peeling it off; I would test that method on the bias edge of some scrap fabric first to make sure it would not distort the seam when you try it. If you are able to successfully remove the fusible, the time to do it would be immediately before layering the quilt sandwich, as you would want to keep that seam stabilized as long as possible.