I would be afraid constantly having a mechanical machine set at that odd zigzag might do some harm to the gears, or whatever makes a machine work. Why not just leave your straight stitch where it is, and mark your 1/4" mark with moleskin, painters tape, post its or whatever works best for you and if your now foot extends beyond that mark.....do your mark before the foot( closer to you)...... I have a 1/4" foot on mine, but I also have a strip of moleskin before the fabric gets to the foot.......as I feed it up to the foot......I'm sure there are tutes on how to find that 1/4"......