|To safely open a buttonhole using a seam ripper, place a pin crosswise at one end of the buttonhole. From the opposite end, gently start slicing open the buttonhole by poking the long tip of the seam ripper through the fabric. Move the ripper towards the pin. The pin will serve as a break so the seam ripper cannot cut through into the threads.
Before using this technique, I would occasionally cut through the threads and ruin the buttonhole. The pin is insurance in case you don't have perfect control of the seam ripper.