Hmmm, their pelvis does slacken off in the run up to kidding, and it is best not to disturb them too in the very latter stages of pregnancy, just in case it stresses them and sends them into early labor. We normally cut their feet for the last time about 4 weeks before they are due, and then wait until a fortnight after they have kidded to do them again. That way it's only a gap of six weeks.
If you feel they need done again in between, I wouldn't worry about doing the front feet, it's lifting the back feet that might put them off balance and make them fall.
Beth