I have been thinking about this since first reading the post. I wonder the purpose of locking the dials. To prevent the machine from changing settings from vibration? To prevent the user from changing settings while straight stitching? I'm guessing the second.
Nevertheless I still thwarted the well intentioned engineering: I used spook pins to lock the dials, put on a straight stitch foot, and fired up the machine. Then I removed the pin locking the stitch width and adjusted it, forgetting to remove the straight stitch foot and, not unlike my operator error with the World's Best Sewing Machine, I promptly shattered a needle on the foot...fortunately I didn't strip any gears or break the timing belt.
It's a good thing I don't do this for a living.