http://www.daystyledesigns.com/freemotionfoot.htm
I leave my darning feet and open toe feet alone and do not alter anything when fmq'ing. Haven't needed to. I have a Babylock and their feet work perfectly for me. So I can't give an opinion about altering them. On my machine, if I set the tension to 0-1.5, lower the feed dogs, adjus the stitch length, use a supreme slider on the machine bed, wear sewing gloves with rubber pads, install a new Schmetz or Organ (on my Babylock Jane) sharp 80/12 needle, use polyester thread (Isacord for me) adjust the presser foot pressure and sew slower while moving the fabric slower for uniform stitches, then my fmq'ing works just fine.