I have needed to do this a few times. And since I pin my backing on the canvas it is easy to remove and reload. I just make sure that I place a safety pin at the center of the backing at the top, a safety pin at the center of the backing at the bottom, and another safety pin at the center of the bottom of the quilt top. I also baste across the sandwich using long wavy lines of stitching about every 8 inches down the length of the sandwich. When I am ready to reload I center the backing and pin to the canvas leaders, pull out the basting stitches, center the quilt top to the canvas leader, roll and smooth everything into place and resume quilting. Has worked good for me.