you do not have to "unpick" the seams but can just leave the stitching in and then sew a 1/4" seam. You can press the seam to 1 side so the 1/8" seam will be OK left in. I would recommend this since sewing 1/8" seam may make your quilt blocks not fit correctly. Also 1/8" may be too thin and pull out if stress in but on the seam. Good luck!!!!!